RECORD: Darwin, C. R. & Emma Darwin. [1864]. Draft of On the sexual relations of the three forms of Lythrum salicaria. CUL-DAR27.2.A1-A54. Edited by John van Wyhe (Darwin Online, http://darwin-online.org.uk/)

REVISION HISTORY: Transcribed by Christine Chua & edited by John van Wyhe 12.2022. RN1

NOTE: See record in the Darwin Online manuscript catalogue, enter its Identifier here. Reproduced with permission of the Syndics of Cambridge University Library & William Huxley Darwin.

Darwin, C. R. 1864. On the sexual relations of the three forms of Lythrum salicaria. [Read 16 June.] Journal of the Linnean Society of London (Botany) 8: 169-196, 1 text figure. F1731


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On the Sexual relations of the three Forms of Lythrum salicaria by

Charles Darwin F.R.S. F.L.S. &c

Some of the species of Lythrum offer in their manner of fertilisation a more remarkable case than can perhaps be found in any other member of the vegetable plant or animal. kingdom.

In Lythrum salicaria, for instance three plainly distinct different forms occur; each of which these is an H hermaphrodite, but each is distinct in its female organs & each is furnished with two sets of stamens or males which differing from each other in appearance & in function, as widely as the stamens or males of distinct species. (a) Two of the three hermaphrodites forms must co-exist, & the pollen be carried by insects reciprocally from one to the other, in order that either of the two should be fully fertile. but unless all three forms co-exist there will be a waste of two whole sets of anthers stamens & the organisation of the species, as a whole, will be imperfect. On the other hand when all three hermaphrodites co-exist, & the pollen is carried from one to the other, the scheme is perfect;— there is no waste of pollen, & there is no false

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(a)

Altogether there are three females & three sets of males, as distinct as if they belonged to different species; of the same genus; & if smaller functional differences are considered, there are five distinct sets of males.

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(The three forms may be conveniently called, from the unequal lengths of their pistils,— the long-styled, mid-styled, & short-styled. Their existence & differences were first observed by Vaucher*, & subsequently more carefully by Wirtgen; but both neither not being guided by any theory, overlooked perceived some of the most curious points of difference. I will first briefly describe the three forms by the aid of the accompanying accurate diagram, which shows the flowers, in six times magnified, in their natural position position, with their petals & the near side of the calyx removed.

(The Diagrams to be inserted here)

The Long-styled form, — This can at once be recognised by the length of the pistil, which is (including the ovarium) fully one-third longer that that of the mid-styled, & more than trice as long as that of the short-styled for. It projects considerably beyond

It is so disproportionately long compared with the flower, that it projects in the bud through the unfolded petals. It projects stands out considerably

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* Hist. Phys. des Plantes d' Europe Tom. ii., 1841, p. 371.2 Wirtgen, Ueber Lythrum salicaria und dessen Formen,— Verhand. des naturhist. Vereins der preuss. Rhein., 5th Jahrgang, 1848, S. 7

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co-adaptation. In short Nature has ordained a most complex marriage arrangement, namely a triple union between three hermaphrodites forms ;—each hermaphrodite being in its female organ & furnished with two sets of males.)

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beyond the longer stamens; its terminal portion depends a little but the stigma itself is slightly upturned: the globular stigma is considerably larger than that of the other two forms. The six longer stamens project about two-thirds of the length of the pistil, & correspond in length with the pistil of the mid-styled form. (a)

The six shorter stamens (each of which alternates with a longer one) lie concealed within the calyx; their anthers are rather smaller than those of the longer stamens; & they are more their ends are upturned, & they they are so more graduated in length, so as to form a sta triple row; both which characters are here much more marked than with in with the longer stamens, which vary in these two respects. The anthers of the shorter stamens are smaller than those of the longer stamens. Knowing that the pollen differs greatly in the longer & shorter stamens of the both the inside and short-styled the two other forms, I carefully compared that of the two sets of stamens in this form: in both the pollen-grains are yellow, but they are a little larger in the longer than in the shorter anthers stamens. The difference is slight, so that I convinced myself of its treble reality only by putting

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(a) The correspondence in length is cut of course mathematically exact, but is generally very close; the stamens often slightly exceeding in this & in the several following cases that length

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(a) The correspondence with the pistil in length in this & the several following cases is generally very close; the difference, where there is any, being usually in a slight excess of the length if n the stamens.

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two small heaps close together under the compound microscope & I found I could (with one exception) always distinguish them: I then showed the specimens to two other persons, & they likewise distinguished them the two kinds & pointed out which were was the largest. The capsules of this form contain on an average 93 seeds: how this average was obtained will presently be explained. A parcel of seed, when cleaned, sti I repeatedly observed that this the seed when cleaned seemed larger than those seed of that from the mid-styled or short-styled forms; consequently I placed 100 long-styled seed of the long-styled in a good balance, & by the double method of weighing found that they equalled 121 seeds of the mid-styled & 142 of the short-styled short; or that in short 5 five long-styled seed equalled 6 equal in weight six mid-styled & 7 seven short-styled seed. These slight differences in the weight of the seed &, as we shall soon see, in the average number number produced, seem are worth recording, as they characterize not mere mere varieties, but always invariably always coexisting forms of the same species.

Mid-styled form.—The pistil occupies the position represented in the diagram, with its extremity* stigma, considerably, but in a variable degree, upturned;

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; in length it is the stigma is seated & placed between the anthers of the long & the short stamens. The longer stamens correspond in length with the pistil of the long-styled form; their filaments are coloured bright pink; the anthers are dark-coloured it but from containing bright green pollen both & from their early dehiscence they general appear emerald-green. Hence the general appearance of these stamens is remarkably dissimilar from that of the longer stamens of the long-styled form. The shorter stamens, enclosed within the calyx, resemble in all respects the shorter stamens of the long-styled form, & both correspond in length with the short pistil of the short-styled form. The green pollen-grains of the longer stamens is are plainly larger than the yellow pollen-grains of the shorter anthers: this fact was well shown plainly conspicuous in several camera-lucida drawings made for me by my son, Mr. W. E. Darwin. There is some variability in size, but 12/7000 of an inch may be taken as about the average diameter of the green pollen-grains when distended with water, and 9/7000 as the diameter of the yellow grains of

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the shorter anth stamens; i.e so that the difference in diameter is in about the proportion of four to three. The capsules contain on an average 132 seeds; but, perhaps, as we shall see, this is rather too high an average. The seeds themselves are smaller than those of the long-styled form.

Short-styled form.—The pistil is here very short, not one-third of the length of that of the long-styled form. It is enclosed within the calyx calyx, which, differently from in the other two forms, does not enclose any stamens anthers. The longer stamens with their pink filam. The end of the pistil is generally bent upwards at right angles. to the lower part. The longer stamens, with their pink filaments & green pollen, resemble in size of the pollen grains & in all respects the longer stamens of the mid-styled form, & both correspond in length with the long-styled pistil. The shorter stamens, with their uncoloured filaments & yellow pollen, resemble in size of the pollen grains & in all respects the longer stamens of the long-styled form, & both

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correspond in length with the mid-styled pistil. The green pollen if f

The capsules contain fewer seeds on an average than in either of the preceding forms, ie namely 83.5, & they are considerably smaller in size. In this latter respect, but not in number, there is a gradation parallel to that of the length of the pistil, the long-styled having the largest, the mid-styled the next in size, & the short-styled the smallest seed.

From this description we see that in there are three forms distinct female organs, or rather females, as they are borne on distinct individuals, differing in the length & curvature of the style, in the size of the stigma, & in the number & size of the seed. In the three forms, taken together, there are thirty-six stamens or males, & these can be divided into three groups sets of a dozen each, differing from each other in length, curvature, & colour of the filaments, in the size of the anthers, & especially in the colour & diameter of the pollen-grains. Each of the three forms bears half-a-dozen of one kind of stamens & half-a-dozen of another kind, but [2 words illeg]

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not all three kinds of stamens. In each form The stamens which correspond in length with a all The three kinds of stamens in differing lengths correspond in length in length one of with the three long pistils; which equally differ in length : the correspondence is always between the pistil of one form, & half-a dozen stamens of the two other forms. half the stamens borne of by two forms with the pistil of the a third form. These remarks apply only as yet to the structure of & not, as yet to the functions of the reproductive organs.—

I ascertained the average number of seed already given produced by each form, by selecting by counting them and in eight of the finest fine selected capsules taken from each plants of the three forms growing wild; & counting the seed ; & the result was, as we have seen, for the long-styled (neglecting decimals) 93; mid-styled 132; & short-styled 83.

I should not have trusted this result, but I had a number of young plants in my garden, which from their youth did not yield the full complement of seed, but they were of exactly the same age & growing grew under exactly the same conditions, & were freely visited by bees: I took 10 six fine capsules from each form, & found the average to be for the long-styled 80, for the mid-styled 97, & for the short-styled 61. Lastly, I made numerous artificial

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unions, & as may be seen in the following tables, to be given that the fertile union these gave in the long-styled an average of 90 seed, in the mid-styled 117, & in the short-styled 71. (a) From this concurrent evidence there can be no doubt that the three forms do produce a considerably different average num number of seed.) & conversely, as the latter ca

(According to Vaucher & Wirtgen, the three forms coexist in various all parts of Europe. Some friends gathered for me in North Wales a number of twigs from separate plants growing at near together each other, & then classified them. My son did the same in Hampshire, & here is the result:—

 

North Wales

Hampshire

Long-styled

95

53

Mid-styled

97

38

Short-styled

72

38

Total

264

129

Total

148

135

110

393

 

If twice or thrice the number had been collected, probably the three forms would have been found nearly equal; I infer this from considering the above figures, & from my son

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So that we have good concurrent evidence of the different [illeg] average production of seed by the three forms. To show that the artificial fertilisation, presently to be detailed, I may here state that the finest given described, produced their full action effect & may be trusted, I may state that one mid-styled capsule thus produced fertilised yielded 151 good seeds, which is the exact number of the finest wild capsule examined by me: artificially fertilised short- & long-styled capsules actually produced a greater number of seeds than I have found in wild plants, but then I did not examine many of the latter. This Lythrum, I may add, offers in a remarkable in instance, how profoundly ignorant we are of the life-conditions of each species: naturally it grows in as was "in wet ditches, watery places, & especially on the banks of streams," & though it produces million so many minute seeds, it never spread on the adjoining land; yet planted in my garden on clayey lyin soil lying over the chalk & which is so dry that a rush will can not grow be found, it thrives most luxuriantly, grows to above six feet in height, & (which is a severer test) is fully as fertile as in a state of nature. Nevertheless it would be almost a miracle to find this plant spontaneously growing in this neigbourhood in on such a situation soil land as my garden, though under its native climate.)

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telling me that if he had collected in another spot, he was felt sure that the mid-styled plants would have been greatly in excess. I several times sowed small parcels of seed, & raised all three forms; but I neglected except in to record the parent-form, except in one instance, in which I raised from short-styled seed nine plants, of which one turned out consisting of 4 long-styled, two mid-styled, & 3 three short-styled.) froms.) pla seedlings

(Insects are necessary for the fertilisation of this species Lythrum. During two years I had kept two plants of each form protected from the insects & the contrast in the autumn they presented a remarkable contrast in appearance with by their in the with that of the adjoining uncovered plants, which were densely covered with capsules. In 1863 a protected a a covered long-styled plant plants (which are were was known to be fully fertile when artificially fertilised) for the long-styled & two mid-styled forms, each produced only five poor capsules; & a short-styled form only one two mid-styled plants produced the same number; & two short-styled plants between them produced only one & the previous year two capsules; all these capsules contained very few seed; yet the plants plant were fully

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productive when artificially fertilised under the net. In a state of nature the plants flowers are incessantly visited for their nectar by hive-bees & humble-bees & various diptera. The nectar is secreted all round the base of the ovarium; but a passage is left only along on the upper side within the calyx formed along the upper & inner side of the calyx by the lateral bending deflection (not represented in the diagram) of the filament basal portions of the filaments of the longer stamens ; so that insects invariably alight on the upper side of the flowers, on the projecting stamens & pistil, & insert their probosces along & bending into along the upper inner margin side of the calyx. Now it may be observed We can now see why the ends of their anthers, & the ends of the pistils with their stigma are a little upturned, namely for both the in order that they may brush against the lower hairy surfaces of the insects' bodies. The short stamen which lie enclosed within the calyx of the long- & mid-styled forms can be touched only by the proboscis & the narrow chin of the sucking bee; hence they stamen have their ends more upturned, & they are made graduated in length, so as to fall into a narrow triple file, their three deep,

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sure to be raked by the thin intruding proboscis. The bas anthers of the longer stamens stand laterally further apart & on are more nearly of the same basal, as length, for they have to brush against the insect body whole breadth of the insect's body. I may here incidentally remark that in very many flowers the pistil, or the stamens, or both, are rectangularly bent to one side of the flower: this bending may be permanent, as with Lythrum & many many others, or may be effected by a temporary movement (as in Dictamnus fraxinella & many others) which takes place with in the stamens occur when the anthers dehisce, & in the pistil by no means always & in the pistil when the stigma is mature; but these two movements are by no means always contemporaneous in the same flower. Now I have found no exception to the rule, that when the stamens & pistil are bent, the bending is exactly to that side of the

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flower which secretes nectar (even though there be a rudimentary nectary of large size on the opposite side, as in some species of Corydalis); or, when when nectar is secreted on all sides, to that side in which where the structure of the flowers allows the easiest access to the section it, as in Lythrum, Papilionaceous flowers, & many others. The rule consequently is that when the pistil & stamens are bent, they anthers & stigma the stigma & anthers are then brought into the gangway pathway towards the nectary. There are a few exceptions cases which seem to be exceptions, but they are not so in truth: for instance, in the stem in some Lilies, & Gloriosa lily is the strongest example, in which nectar is secreted at the base of all the pistil, & the pistil is bent at right angles to one side; but

Gloriosa lily, the stigma of the grotesque & rectangularly bent pistil is thus brought, come not into the pathway from the open air towards the nectar-secreting recesses of the flower, but into the circular path route from one nectary to the other; in Scrophularia aquatica

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the pistil is bent downwards from the mouth of the flower, but it thus strikes the pollen-dusted breasts of the wasps which habitually visit its these ill-scented blooms. In the above rule above given is only we see one more instance of the supreme dominating power of insects over all the minor structural details of the structure of flowers, especially of those which have irregular corollas. through the co-adaptation of the flower to the insect, & of the insect to the flower. Flowers which are fertilized by the wind must of course be excepted, but I do not know of a single instance of an irregular flower which is fertilized or crossed by this agency.)

(I have delayed too long on these points, but I must allude to one other. We have seen that the three pistils of different lengths have each two half-dozen sets of stamens of corresponding length. borne by the other two forms. When bees suck the flowers, the longest stamens, bearing the green pollen, rub against the abdomen & the interior sides of the posterior legs, as does likewise the stigma of the long-styled form.

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The stamens of the middle length & the stigma of the mid-styled form rub against the under side of the thorax & between the front pair of legs. The shortest stamens & the stigma of the short-styled form must rub against the proboscis & chin; for the bees in sucking insert only the front of their heads within into the calyx.

On catching bees, I observed much green pollen on the inner sides of the hind legs & on the abdomen, & much yellow pollen on the under side of the thorax. There was also pollen on the chin, and, it may be safely presumed on the proboscis, but this was difficult to observe. I had, however, independent proof that pollen is carried on the proboscis; for in a covered protected short-styled plant (which produced only two capsules) when protected from insects) one small branch was accidentally left during many days pressing against the fine net, & bees were seen sucking inserting their probosces close through the meshes, & I found that in consequence numerous capsules had largely swollen were formed on this one small branch.—

Hence From these several facts it follows that insects would chiefly carry carry to each the stigma of each form,

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pollen from the anthers stamens of corresponding length; & we shall presently see the importance of this circumstance adaptation. It must not, however, be supposed that the bees do not get more or less dusted with more or less all over with the several kinds of pollen of all kinds ; they certainly do, as could be seen with the green pollen from the longest stamens. Moreover, at a case will presently be given of a long-styled plant which grew absolutely by itself, & which produced an abundance of capsules, which must have been fertilised by its own two kinds of pollen; but these capsules contained a very poor average of seed.

Hence insects, & chiefly bees, act both as general carriers of pollen, & as special carriers of the right kind*.

Variability. — Before passing on to more interesting important topics, I must say a few words on this head. Wirtgen* remarks on the variability of L. salicaria in hairiness in the branching of the stem, in the presence of the arrangement of length of the bracteæ, size of the flowers petals, in the arrangement & in many several (a)

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(a) text

other respects; the plants now growing in my garden have their leaves arranged oppositely, alternately & in whorls of three; & differ greatly in shape.

The stems of the plants bearing leaves in whorls are hexagonal; those of the other plants are quadrangular.

* Verhand. des naturhist. Vereins, 5th Jahr, 1848, p. S. 11, 13—

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* (a) Footnote to p. 13

In my paper on the two forms of Primula (Journal Proc. Linn. Soc. 1862, p. 85) I stated that I had only occasionally seen Humble-bees sucking the flowers of the Cowslip (P. veris). Since then I have had some beds in my garden containing nearly 700 plants, & these were incessantly visited by Bombus hortorum & B. muscorum. I caught some & in [illeg] themselves I found that (as I had anticipated ( p. 86) that near a vast majority of the pollen-grains which adhered to the base of the proboscis were large-sized & had come from the longer long stamens of the short-styled form, & were thus placed ready to fertilise the stigma of the long-styled form. On the other hand, on towards the middle & tip of the proboscis, a very large proportion of the pollen-grains were nearly all of the small size, & had come from the shorter short stamens of the long-styled form. My son caught, also, a moth (the (Cucullea verbasci) hovering hovering over the bed, & observed I found on its proboscis the same a similar distribution of the two kinds of pollen-grains. as w I give these facts as a further illustration of the importance of the relative lengths of the stamens & pistil.

[In another hand:] This footnote is in the printed version, attached to p. 16 (marked*)

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other respects. But we are concerned only with the reproductive organs: the upward bending of the pistil is variable, & in a remarkable degree in the short-styled form, in which it is sometimes straight, sometimes slightly curved, but generally upturned at right angles. The degree to which the longer two sets longer & middle stigma large stigma of the long-styled pistil lies generally frequently has longer papillæ or is rougher than that of the mid-styled, & this is rougher than that of the short-styled form; but this character is appar, though fixed & uniform with the two forms of Primula, is here variable, & I have seen a mid-styled stigmas quite rougher than those of the long-styled. The degree to which the longer & middle stamens are graduated in length & are upturned at their ends is variable; sometimes all are equal. The colour of the green pollen in the long stamens is variable* & is sometimes pale greenish yellow; in one short-styled plant it was almost white. The grains vary a little in size: I have seen examined one short-styled plant with the grains above the average size; & I have seen a long-styled plant with undistinguishable from the grains from in the longer & shorter anthers. We have here considerable fluctuations of character; & if any of these slight structural differences

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* note to p. (17)

 Lagerstrœmia Indica, one of the Lythraceæ, is strangely variable in its stamens, I presume in part in part due to its inclosed conditions in the hot-house growth cultivation in a hothouse

The most perfect flowers produced with me five very long stamens with thick flesh-coloured filaments & green pollen, & from 19 to 29 short stamens with yellow pollen; but many flowers produced only one, two or three, or four long stamens with green pollen, which in some of the anthers was was sometimes wholly replaced by yellow pollen; one anther offered the singular case of half one half or one cell being filled with bright green & the other half with bright yellow pollen. One petal had a furrow near its base, which contained pollen. According to analogy with Lythrum, this plant species would produce three forms; if so, the above plant was the a mid-styled form: it was quite sterile with its own two kinds of pollen.

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were were of direct service to Lythrum the plant or were correlated with functional differences, we can see that the preservation & accumulation might readily cause an appreciable species is just in that state in which natural selection could might readily do much for its modification.)

(As far as structure or external appearances are concerned (We have seen that there are three kinds of females & three kinds of males organs or stamen; each kind kind of the latter being placed in two borne by half-dozens in two of the forms. It remained to discover whether these several sexes or sexual organs differ from each other in function. No one fact brings more prominently forward the complexity of the reproductive system of this extraordinary species plant, than the necessity, in order to ascertain the from its function above fact, of artificially making eighteen distinct unions. Thus the long-styled form had to be fertilised with pollen of from its own two distinct kinds of anthers, from the two in of the

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mid-styled, & from the two in the short-styled form. The same process had to be repeated with both the mid- & short-styled forms. It might have been thought sufficient to have tried on each stigma for instance, the green pollen, for instance, from either the mid- or short-styled longer longer stamens, & not from both; or each stigma; & so will the two other kinds of stamens; but the result proved that this would have been insufficient, & that it was necessary to try all six kinds of pollen on each stigma. As in artificial fertilisation there will always be some failures, it would have been advisable to have tried repeated each of the eighteen unions a score of times each ; but the labour would have been too great; as it was, I made 223 artificial unions; i. e. I tried fertilised, on an average, above a dozen flowers in the eighteen necessary different methods. Each flower was fertilised castrated; the adjoining buds had to be removed, that the marking marking-thread, wool &c might be safely secured secured; & after each fertilisation the stigma had to be examined with a lens to see that there was sufficient pollen. Two Plants of all three forms were protected either during either [illeg] both during two

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years were protected by large nets on a framework; & were fertilised in order f two were taken plants were used during either one or both years in order to avoid any individual peculiarity in any one plant. As soon as the flowers withered, the nets were removed; & in the autumn the capsules had to be were daily inspected; when ripe the seeds were ripe they were counted under the microscope. I have given these details that some confidence may be placed in my experiment; & as possibly of some service to any further observer the following tables; and as some excuse for two supposed blunders which, I believe I made. These are referred to with their probable causes in two notes to the Tables; they the erroneous numbers are given entered in the tables that it may not be supposed that I have in any one instance tampered with the results. The above d

(A few words explanatory of the thr three Tables must be given. Each is devoted to one form & is divided into six compartments. The two upper compartment ones in each case table give the product of good seed from the application of

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pollen from the two sets of stamens which correspond in length with the pistil of that form & which are borne by the other two forms. The two lower next lower lower compartments show the result of pollen from the other other two sets of stamens, borne by the above two forms which do not correspond in length with the pistil, & which are borne by the same two forms. The two lowest compartments show the result from the appl of the two pollen produced th of the application of the each form's own two kinds of pollen.

The term "own pollen," have used here & in the tables does not mean pollen from the flower to be fertilised, for this was never used; but from another flower on a same plant or more more commonly from a distinct plant of the same form.

In the result given, "0" generally means either that no capsule was produced produced, or that the capsule contained no good seed. In some part of each row of figures in each compartment, a short horizontal line may be seen; the unions above this line were made in 1862, & below it in

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1863: it is of importance to observe this, as it shows that the same general result ensued in two successive years; but more especially because 1863 was a very hot & dry season & the plants had occasionally to be watered. This did not prevent the full complement of seed being produced from the more fertile unions; but it rendered the less fertile unions even more sterile than they otherwise would have been: I have seen striking instances of this same fact in the making homomorphic & heteromorphic unions in Primula*(a); & it is well known that in making hybrids, the conditions of life must be most highly favourable otherwise there is no chance to give any hope chance of producing producing hybrids from the species which can be crossed cross with difficulty.)

(à Mr Norman, you must end your page here, for 4 sheets have to be here introduced & your next page will be from figures in advance. The note *(a) has not been sent.)

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* Footnote to p. 17

In the spring of 1862 I crossed a number of forty cowslip flowers (P. veris) heteromorphically & homomorphically. The plants were accidentally exposed in the greenhouse to too hot a sun, & a number of umbels suddenly perished. Some, however, remained in fairly moderately good health, & on these there were twelve flowers which had been fertilized heteromorphically & eleven which had been fertilized homomorphically. The twelve heteromorphic unions yielded seven fine capsules, containing on an average 57.3 good seed. Now mark the difference, the eleven homomorphic unions yielded only two capsules, of of which one contained 39 seeds, but so poor, that I do not suppose one would have germinated, & the other only 17 fairly good seed. It made this would be superfluous to give any b more details on this experiment, or on some which I made at the same time on with P. Sinensis Sinensis, since after the reading appearance of Mr. John Scott's admirable paper on the various dimorphic species of Primula, in which he confirms my former conclusions results & adds many original and valuable observations. Dr. Hildebrand has also (Botanische Zeitung, 1864, Jan. 1, S. 3) confirmed my general results with respect respect to P. Sinensis, & has corrected an error, into which in some unaccountable man manner I fell, namely, the statement that the pollen-grains from the long- &

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*(a) Foot-note continued to p. 13 to p. 17

short-styled forms are were of the same size. Dr. Hildebrand has added a series of new & important experiments experiments, for he fertilized homomorphically a number of flowers with pollen from the same form, & likewise from the same individual flower. These latter he found were thus rendered rather more sterile. This experiment, has never been systematically tried before. but accords with the belief of the most experience

[23-26]

[missing]

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Summary of the three preceding Tables.

Long-styled form,— 26 flowers were fertilised by the stamens of corresponding in height length borne by with the pistil, of in the mid- & short-styled forms, & they yielded 61.5 per cent of capsules, The capsules which contained on an average 89.7 seed.

(26 flowers were fertilised by the shorter other & shorter stamens of the mid- & short-styled forms, but they were too other sterile for any average yielded only two very poor capsules.)

(a) 30 Flowers well fertilised by bees by [illeg] both their own kinds sets of after one own this stamen of this long-styled form, or by one set produced many capsules, containing on an average 21.5 seed.)

Short-styled form.—25 flowers were fertilised by the stamens of corresponding length in borne by the long & mid-styled forms, & they yielded 72 per cent of capsules, The capsules which (excluding one capsule with only 9 seed) contained on an average 70.8 seed.

(20 flowers were fertilised by the longer stamens of the long & mid-styled forms, but they yielded only two very poor capsules.)

[27v]

(a) (30 flowers fertilised by this form's own own two sets of stamens yielded only eight very poor capsules. But flowers well fertilised by bees by one or both own kinds of pollen, produced more numerous capsules, containing on an average 21.5 seed

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(20 flowers were fertilised by the both the stamen kinds of their own kinds of sets of stamens frequently yielded only two poor (or perhaps three) capsules.)

Mid-styled form.— 24 flowers were fertilised by the stamens of corresponding length in borne by the long- & short-styled forms, & they yielded 96 (probably 100) per cent of capsules, The capsule which excludes (excluding one capsule with 12 seed) as this gives fairest average contained 117. on an average, 117.2 seed.)

(15 flowers were fertilised by the longer stamens of the short-styled form & they yielded 93 per cent of capsules, These capsules which (excluding 4 capsules with less than 20 seed) as this gives the fairest average) contained on an average 102.8 seed.

(13 flowers were fertilised by the shorter stamens of the long-styled form, & they yielded 54 per cent of capsules, These which capsules (excluding one with less than 20 19 seed) contained on an average 60.2 seed.)

(12 flowers were fertilised by own longer stamens & they yielded 25 per cent of capsules, These capsules which (excluding one with less than 20 9 seed) contained, on an average, 77.5 seed.)

(12 flowers were fertilised by own shorter stamens, & they yielded not a single capsule.)

(29

(29

Considering & the three Tables & this summary, we may safely draw the following conclusions. First, that as in structure so in function, there are three females or female organs; this is clear manifest, for when they all three receive the very same pollen, they are acted on most differently that same pollen, which produces a full crop of capsules when applied to the own stigma, for instance to that of the long-styled form is powerless or nearly powerless when applied to on the stigmas of the other two forms mid-styled short-styled. So conversely with the thirty-six stamens, which are divided distributed between the three forms, we know that they consist of three separate sets of a dozen each differing in several various respects; & in function the pollen of these three sets when each kinds of stamens applied to the very same one & the same stigmas acts most differently; as a glance at the tables proves. But we shall presently see that the action of the pollen of the whole dozen longest & of the whole dozen shortest stamens is not identical.) This being some difference o the half dozen of each of their kinds, which are borne by the distinct separate forms.

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(30

Secondly, we see that only the longest stamens fully fertilise the longest pistil, the middle stamens the middle pistil, & the shortest stamens the shortest pistil. And now we can fully comprehend the meaning of the almost exact correspondence in length between the pistil of each form & the two half-dozen sets of stamens in borne by the two other two forms; for the stigma of each form is thus rubbed against the same spot of the insect's body, which becomes most charged with the proper pollen. In all three forms, the female organ is but feebly feebly, or not at, all acted on by the its own two kinds of pollen. borne by

In my papers on the dimorphism of Primula & Linum, I used the terms "heteromorphic" for the fully fertile unions between the female element of the one of the one form & the male element of the other, and "homomorphic" for the less fertile or quite sterile unions unions between the female & male elements of the same forms form.

The principle involved involved in these terms holds good for with Lythrum, but is insufficient; for though in with each of the three forms the fertile unions are all

(31

(31

heteromorphic, the appropriate pollen being taken from one or the other coming from the correspond stamens of corresponding length borne by the other two other forms, and though the homomorphic unions of each the females with it their own two sets of males are all more or less sterile, there remain in each case two other sterile unions, not included in these two terms. Hence it will be found convenient to designate in evidence the two unions of the each female with the pollen stamens of the corresponding length, which are fully fertile, as natural & fertile legitimate unions, and the four other more or less sterile unions of each female with the four other sets of stamens, which were more or less sterile, as unnatural illegitimate unions. Consequently, of the eighteen possible possible unions six are fertile & natural legitimate or fully fertile; & twelve are unnatural or in same d illegitimate sterile.)

(Another & curious resemble pollens from the table conclusion cannot be considered as demonstrated, proved, but is rendered highly probable, by the tables. to demonstrate it a score or seven unions of each kind would be necessary.

If we look to the results of the four unnatural & more or less sterile unions under each of the

(32

(32

The unions from of the stamens pistils & pistil stamens of equal length are alone fully fertile: now with the several illegitimate unions it will be found that the less the inequality in length between the pistil & stamens, the greater the sterility of the result. There is no exception to this rule.

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(32

three forms, we shall find no exception to the rule that the sterility is the greater in proportion to the inequality of length between the pistil & stamens used in each union. Thus, with the long-styled form, its own shorter stamens are far more unequal less equal in length compared with to the pistil than its own longer stamens; & the capsules fertilised by the pollen of the shorter stamens yielded fewer seeds: so it is with again the same result follows from the use of the pollen of the shorter stamens of the short mid-styled form which are much more m shorter th than the shorter stamens of the short-styled (see diagram) & the, & therefore more unequal less equal in length relatively to the long-styled pistil. of the long-styled form.

We shall see exactly the same result if we look to the four unnatrural illegitimate unions under the mid- & short-styled forms. Certainly the difference in sterility in these several cases is very slight, but would a but it is the fertility of each union always decreases always in some direction more parallel but the sterility always increases with the increasing inequality of length between of the stamen & pistil & the stamens which are used used in each case union. Therefore I believe in the above rule

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(33

; but to prove it, would require a vast number of artificial unions. If as I believe the rule be true, probably we must probably look at it as an incidental & certainly useless result of the great principle of gradational changes through which this species, like all others has passed through in arriving at its present state condition. On the other hand, the correspondence in length between the pistil of each form & those stamens which alone give cause full fertility is clearly of service to the species, & is probably almost certainly a case of the result of direct adaptation.

Some of the unnatural illegitimate unions yielded, during neither years, as may be seen in the tables, during neither year a single seed; but, judging from the case of the long-styled plant, it is probable probable, if they such unions could be effected repeatedly under the most favourable conditions, some few seeds would be produced. Anyhow, I can state that in all the eighteen possible unions the pollen-tubes penetrated, after 18 hours the stigma. I have

(34

(34

reason to believe that the offspring from the unnatural illegitimate unions present some singular characteristics; but until my observations on this head are repeated, I must be silent. At first I thought that perhaps two kinds of pollen placed together on the same stigma might pr would give more fertility than any one kind; but we have seen that this is not the case with each form's own own two kinds of pollen; nor nor is it probable in any case, as I occasionally got by the use of single kinds of pollen fully as many seed as more rather more = seed than, I have seen in a capsule naturally fertilised. Moreover the proper pollen from a single anther is more than sufficient to fully fertilise each stigma; hence, in this as in so many other cases, at least twelve times more as much of each kind of pollen is produced, as is necessary to ensure full fertilisation.* From the dusted condition state of the bee's bodice which I examined, there whole body of the bees, which I examined,

(35

(35

can be hardly any doubt that it is probable that some pollen of all kinds must be will is deposited on each all three each stigma; but there can be hardly be any be a doubt that the pollen of the stamens of corresponding length will be prepotent & will wholly obliterate any effect of from the other kinds of pollen, even if previously deposited on the stigma. I infer this partly partly from the fact ascertained by Gärtner that each species' own pollen is so prepotent over over that of another any other species, that if put on the stigma many hours subsequently, it will entirely obliterate the of action of the foreign pollen. But I infer it draw the above inference especially from the following experiment: I fertilised, homomorphically or unnaturally illegitimately some long-styled cowslip flowers (Primula veris) with their own pollen, & exactly 24 hours subsequently I fertilised these same stigmas heteromorphically or naturally legitimately with pollen from a the other form of short-styled dark-red polyanthus. I must premise that I have raised many seedlings from crossed cowslips & polyanthus & know their peculiar appearance; & I further know, by the test

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(36

of the fertility of the mongrels inter se, & with both parent forms, that the Polyanthus is a variety of the cowslip, & not of the primrose (P. veris vulgaris) as some authors have supposed. Now from the long-styled cowslip thus twice fertilised, as above explained, I raised 29 seedlings, & everyone of them was had flowers coloured more or less red; so that like the ordinary mongrels from the cowslips & polyanthus; not one from cowslip was raised the heteromorphic polyanthus-pollen wholly obliterated the influence of the few homomorphic pure cowslip pollen, & not a single pure cowslip was produced.

(The third & last 2 cowslip main conclusion which may be deduced even from, even from a glance the Table, even from a glance at them, is that the mid-styled form differs from both the others in its much higher capacity to be for fertilisation. by several kinds of pollens. Not only did the 24 flowers, naturally fertilised by the stamens of corresponding lengths all, or all but one, yield capsules rich in seed; but of the other four unnatural illegitimate unions,

(37

(37

that by the longer stamens of the short-styled form was highly fertile, though less than in the two natural legitimate unions, & that by the short stamens of the long-styled form was fertile to a considerable degree; the two unions with this form's own own pollen were were sterile, but in different degrees. By comparing first compartments III & VI & then IV and V in this table, we learn we learn a remarkable fact, namely, that though the long short stamens with their & green pollen are identical in appearance on all short-short stamens and their respects, in pollen of from the short stamens themselves of the long-styled & own mid-styled forms used in these two unions [illeg] is identical in appearance structure, size & colour in all respects yet that their its action is widely different; in the one case above half the fertilised flowers yielded capsules containing a fair average number of seed; in the other case not one single capsule was produced. So, again, the in the the green large-grains of the long stamens with their large-grained green pollen of the short-styled & mid-styled forms, with their green large pollen-grains is identical in all respects, but their its action, as may be seen in compartments IV & V, are is widely different. In both these cases the difference in action is so plain that it cannot be mistaken, but it can be corroborated: if we look first to Table III, to the legitimate union legitimate action of the

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(38

short stamens of the long- & mid-styled forms (the same in as used in the compartments III. & IV. of Tab. II.) on the pistil of the short-styled form we again see a similar but slighter difference,— in the pollen of the se short stamens of the mid-styled form yielding a smaller average of seed during the two years of 1862 & 1863 than that from the short stamens of the long-styled. Again, if we look to Table I to the legitimate action of the green pollen of the two sets of long stamens, we shall find in every respect exactly the same result, viz that the pollen of the long stamens of the mid-styled form yielded during both years fewer seeds than that from the long stamens from the short-styled form. Their Hence it is certain that the two both kinds of pollen produced by the mid-styled form are less potent than the similar pollens produced by the exactly corresponding stamens of the two other forms.)

(When we remember that the capsule of the mid-styled form yield a considerably considerably larger average number of seed than those of the other two form; when we see that the in the legitimate unions how surely the flowers are more freely surely fertilised in the legitimate unions, & how much more more productive the

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(39

illegitimate unions are than those of with the other two forms, we are led to consider consider the mid-styled form as eminently feminine in its nature. And, although it is impossible to consider as rudimentary or aborted call the two perfectly developed stam the sets of stamens of those of the mid-styled form forms which produce an abundance of perfectly well-developed pollen, in this forms forms mid-styled yet we can hardly avoid connecting, as balanced, the higher efficiency of the female organ with the lesser potency of both the two mid-styled pollens.) in this mid-styled form.

However this may be we now positively know positively

(Finally, it is proved by the Tables that Lythrum salicaria habitually produces or consists of three females different in structure & widely different in function; that it produces or consists of three sets of males equally widely different in structure & function; & that two of the three sets of males are subdivided into subgroups of half-a-dozen each, differing in a marked manner in potency, so that habitually regularly five kinds of pollen are elaborated by this one species of Lythrum.)

[40A]

about one-third of the length of the calyx at beyond its mouth, & stam longer & is therefore half-dozen shorter than in L. salicaria; the stamen, wh globose & hirsute stigma is larger than that stigma of the other two forms; the longer stamens, which are graduated in length, have their anthers standing both just above & just below beneath the mouth of the calyx; the half-dozen grad shorter stamens rise rise rather above the middle of the calyx. & are therefore longer longer than the homologous short stamens in the long-styled the L. salicaria. In the mid-styled form the stigma projects just above the mouth of the calyx, & stands almost on a level with the longer stamens of the previous previous form; the shorter anthers correspond with the same in shorter in the long-styled form its own longer stamens project well above the mouth of the calyx & stand a little above the level of the stigma of the long-styled form; the shorter stamens correspond in all respects with the shorter ones ones in the previous previous form. In the short-styled form the stigma of the pistil is nearly on a level with the anthers of the shorter anther stamen in the two preceding forms; & the longer stamens correspond with the longer stamens of the mid-styled form, & the shorter stamens with the longer stamens of the long-styled form. In short, there is a close general correspondence in structure between this species & L. salicaria, but

(40

(40

Lythrum Græfferi.—I must now say a few words words about some of the other species of the genus. I have examined several numerous dried & half expanded flowers of this new species L. Græfferi, each from a separate plant, kindly sent me from Kew. under these circumstances the following remarks must be received with caution. This species, like the last L. salicaria, is trimorphic, & the three forms apparently occur in about equal numbers. In the long-styled form the pistil projects some little half-a-dozen distance beyond the calyx, & there are corresponding long stamens of corresponding length in th mid- & short-styled forms. In the mid-styled forms the stigma is seated within but near the mouth of the corolla calyx, & in the short-styled low down within the calyx; in each case there are stamens of corresponding length in the other two forms. So that in this species two of the three pistils are included within the calyx, instead of one as in L. salicaria, & two double sets of stamens are likewise included. This fact brings well out the importance of the correspondence in length between each pistil & two two sets of stamens, In the

[41A]

(40a

mid- and short style form the pollen-grain when distended from the longer stamens are were had described nearly double the diameter of those from the shorter stamens; so that there is a greater difference in this respect than in L. salicaria. In the long-styled form, also, the difference though in diameter between the pollen-grains of the longer long & shorter stamens was plainer than in L. salicaria. (a) Altogether there is a close general correspondence between trimor trimorphic of L. Græfferi & salicaria.

Lythrum thymifolia.—This form, according to Vaucher* is dimorphic like Primula & therefore presents only two forms. I received two dried flowers from Kew, which by good which I believe to have been correctly named. Then by good chance presented presented two forms: in the one form the stigma projected far beyond the calyx, in the other it was included within the calyx; in this latter form the style was only one-fourth of

[41Av]

* Hist. Phys. des Plantes d' Europe Tom. 2, 1841, p. 369, 371.—

(a) text

These comparisons, however, of the size of the pollen-grains, must be received with caution, as they were made on specimens long kept in a dried condition.)

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(41

with some differences the organs having in the proportional lengths of the parts. Nevertheless the fact of the each of the three pistils having two sets of stamens, borne by the two other two forms, of corresponding lengths comes comes out conspicuously.— In the (distended)

(42

(42

the length of [2 words illeg] the style of the other form. There are only six stamens; these are are somewhat graduated in length, & in the short-styled form the anthers stand a little above the stigma, but yet do not the stamens by no means equal in length the pistil of the long-styled form; in this latter form the long-styled form the stamens are rather shorter, & near than in the other short-styled other form. These six stamens alternate with the petals, & correspond homologically with the longer stamens of L. salicaria & L. Græfferi.

As there are only six stamens, it is scarcely possible that this species can be trimorphic.—

Lythrum hyssopifolia.—This several species is said by Vaucher, but I believe erroneously, to be dimorphic. I have examined dried flowers from 22 separate plants, & they were all alike; & it is improbable a scarcely probable in light degree that I should then should all have been the same form: if two forms really occur. The pistil is short, with

There are from 6 to 9 stamens graduated in length; there which are occasionally three, which vary in being present.

[42A]

from various localities, kindly sent to me by Mr. Hewett C. Watson, Prof. Babington & others. These were all essentially alike. Hence the species cannot be dimorphic. The pistil varies somewhat in length, but when unusually long the stamens are likewise generally long; in the bud the stamens are short: perhaps these cause circumstances deceived Vaucher. Hence it is scarcely impossible that this

There are from six to nine stamens, graduated in length, those the stamens of which the are which presences in variable in being present

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(43

or always absent correspond with the six shorter stamens of L. salicaria & with the six which are absent in L. thymifolia. The stigma is included within the calyx & stands on a level with in the midst of the uppermost anthers of the longer of stamens, & would generall apparently be generally self be fertilised by them; but as the stigma & anthers are upturned, & as, according to Vaucher, there is a passage left in the upper side of the flower to the nectary, there can hardly be a doubt that the flowers are visited by insects which would occasionally bring pollen from other flowers of the same or of any adjoining plant, as surely as will certainly occurs with the short-styled L. salicaria, (a) According to Vaucher and Lecoq* this species which is an annual generally gives grows almost solitarily, whereas all the three preceding species are social; & this alone would almost have convinced me that L. hyssopifolia cannot be dimorphic, as all forms such plants cannot commonly habitually live by themselves any more better than one sex of a diœcious plant species.

(Hence we see that in this one genus of

[43v]

(a) (text) of which the pistil & the corresponding stamens closely resemble those of L. hyssopifolia.

* Geograph. Bot. de l'Europe, Tom. VI. (1857) p. 157.

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(44

Lythrum, we have trimorphic, dimorphic, & monomorphic species.)

(The inquiry naturally arises, why do these species differ so remarkably in their sexual relations?— of what service can in reciprocal dimorphism & or trimorphism be to certain species, whilst other species of the same genus are present like the great majority of plants, f are monomorphic & present only one form? alone?

I have elsewhere given but too briefly the general grounds of my belief that with all organic beings distinct each individual at least occasionally cross at least occasionally with a distinct individual*: and reciprocal dimorphism is plainly one most efficient means for ensuring this result. (a) But this result are most be is however reciprocal at the very high a cost of occasional sterility (a) in again a lesser degree, from the use not only of each flower's own pollen, but from the use of that of half the individual plant of the species. In that extensive

class of plant, called by C. K. Sprengel dichogams, many of which & I have observed many of others, in which the pollen of each flower is shed before its own stigma is ready, or in which the stigma (though this case occurs more rarely) is mature before the flower's own pollen is ready, sterility partial sterility most often result sterility can hardly fail to be the occasional result;

[44v]

This result it would appear to be one of high importance, for with dimorphic plants it is ensured at the risk of occasional sterility: Even not only is the pollen of each plant is useless or nearly useless to that plant individual, but so is the pollen of half the individual all the plants of the same form with it;—that is, of half the total number of individual plants. In that extensive

[44] (a

(a

Footnote to p. 34

* Origin of Species 3d edit. p. 101.─ Hugo von Mohl has recently (Bot. Zeitung 1863 S. 309, 321) in a most interesting paper advanced the case of the minute, imperfectly developed, closed & self-fertile flowers borne by Viola, Oxalis, Impatiens Campanula &c, as an argument against my doctrine that no species is self-fertilized for perpetuity. I may state that in the spring of 1862 I examined several some of these flowers, it would be presumptuous & superfluous in us to say that which Hugo von Mohl observations are correct, & saw, though less carefully thoroughly, all that H. v. Mohl has so well described. I can add only one remark, which I believe is correct, that in Viola canina, there is an open passage channel for the pollen-tubes from from the ovarium the extremity of the stigma to the ovarium; for I gently pressed a minute bubble of air repeatedly backwards & forwards from end to end. Though the minute & the perfect flowers are so different in structure, it is a rather curious case of correlation, that in the double purple violet (V. odorata?) there are the minute imperfect flowers are double to the very centre core & offspring so that a section appears like the head of a cabbage when cut through. There can be, as von Mohl asserts, no doubt that these flowers are always self-fertilized

[In another hand:] footnote to p. 44, marked *

[44] (b

(b

Footnote to p. 34 continued

,but ; they are are moreover specially adapted for this end, as may be seen in the remarkable difference in the shape of the pistil in V. canina (& in a less degree in V. hirta & V. odorata) * as in more strikingly been in the wonderful form as compared with that of the perfect flower; and in the pollen-tubes, preceding which proceeding from the grains within the anthers in V. canina, & from & from within the lower anthers of Oxalis acetosella, of directing which direct have the wonderful power of directing their course to the stigma. If these plants had had out produced only the minute, closed flowers alone, the proof would have been perfect that they could never have crossed cross with another other individuals. but as the case stands I cannot see how the production of these flowers invalidates my doctrine that no species in perpetually self-fertilised, more than fr the multiplication of other species many plants by bulbs, or stolon 7c.─ As I observe that the production of seed by the perfect flowers of Viola is spoken of as something capricious & accidental, I may state that, although it varies much in different years, it depends exclusively on the visits of bees: I ascertained this by marking many individual flowers thus visited & finding that they produced capsules & by covering up many flowers which (excepting a few

[44] (c

(c

Footnote to p. 34 continued

that I artificially fertilized) did not produce a single capsule. After bees have visited these flowers, the pollen may be seen scattered on the papillæ & on the stigma itself, when bees visit these flowers & they can hardly thus fail thus to cross th distinct individuals. These remarks apply to V. canina, hirta & odorata: in with V. tricolor the case is somewhat different; but I must not enlarge any more on this subject. The production by so many plants of open & perfect & of imperfect & closed flowers seems to me to throw much light on many points: it shows how extremely extraordinarily little pollen is really necessary for full fertilization (I ascertained with V. canina that the perfect & imperfect flowers produce yielded the same average number of seeds): it shows us that well closed flowers fertilisation can be perfectly effected perfected in closed flowers; it shows us that large, highly coloured petals, perfume, & the secretion of nectar are by no means indispensable for [illeg] this same process,

[44] (d

(d

Footnote to p. 34 continued

even in those only species which properly possess base these qualities characters. It seems to me that the necessity of an occasional cross explains the universal presence of at least some flowers fully open flowers, at the expense of the injury from rain & the loss of much pollen by innumerable pollen-robbing insects; it explains the curios enormous superfluity of pollen liable from its liability to loss from these causes, & during conveyance from flower to flower; it explains the use of (excepting in plant fertilise) of a gaily coloured corolla, & perfume, & & nectar namely to attract insects,─ except in those comparatively few cases in which wind is the agent & in which the last-named attributes are deficient.

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(45

; and it would be the inevitable result with both dichogamous & reciprocally dimorphic flowers unless pollen were carried by insects (& nearly in some few species by the wind) from at least flower or plant to the other. As with reciprocal dimorphism, so with dichogamy some species some species within the same genus same species are some of the species are & some are not thus characterized. & some are not

Again in the same genus, as in that of Trifolium, some species absolutely require insect insect-aid to set produce seed, others are qu fertile without an any such aid; now when insect aid is required pollen from other flowers can hardly fail to be generally applied to the stigma of each flower insects are requisite for fertilization, pollen will generally be carried from one flower to the other.

We thus see, that in the same genus by means of reciprocal dimorphism, of dichogamy, & insect-aid, that some species require, or at least receive, incessant crosses with other individuals of the same species; whereas other species of the same genera are can be, & probably of are generally often fertilised during long periods their male element of by the own pollen of their own flowers. Why this should be wide difference in the frequency of crosses should exist occur we are profoundly ignorant. I will only further remark on this head, that it would be a great mistake to suppose that many flowers, which are neither reciprocally dimorphic nor dichogamous

(46

(46

, nor require insect-aid for their fertilization, nor show any particular adaptation in their structure for the visits of insects, are not habitually crossed with the pollen of other plants; this occurs for instance habitually with cabbages, which nevertheless are perfectly fertile (as I know by trial) with their own pollen without aid of any kind.)

B( It But it may further asked, granting that reciprocal dimorphism is of service by ensuring at each generation a cross (but I am far from pretending that it may not have some other additional quite unknown signification), why did not dimorphism suffice for L. salicaria and Græfferi? why were they rendered reciprocally trimorphic, entailing such complicated sexual relations? We cannot answer, except perhaps so far otherwise so far as this is short :—if we suppose a single two plants of the Lythrum L. salicaria to be growing somewhat remote from other plants by themselves, then if the species was only were dimorphic it would, only be [illeg] even only two to one chance that was then two plants against both turning out to be the same form & therefore both consequently being nearly sterile; whereas all that being nearly sterile whereas only be an equal chance in former of the two being turning out different forms & the two being consequently both being fertile;

(47

(47

but as the species is trimorphic & each form can fertilise the two other forms, it is from two to one against both in favour of the two turning out to some different forms & both being consequently both being sterile fertile. We can thus see how reciprocal trimorphism is an may be must be an advantage; & probably it would be more advantageous to this Lythrum, which commonly grows in grows in almost are almost a single files files row along the banks of streams, than in the case of primrose it would be to primroses or cowslips which have neighbours neighbours on all sides.

 

Independently of the service thus apparently rendered by trimorphism we never ought to marvel of any operation being performed or any good gained by the most complex means: But if trimorphism would might effected no good not but all was gained by dimorphism will not to be compared at its existence: for we certainly not in fact to be viewed as anything marvellous was if it gained see through with the case and gained by the most [3 words illeg]

But even even if trimorphism effected no good beyond that gained by dimorphism, we ought not to be feel any feel much surprised at its occurrence, for we continually see throughout nature the same end gained by the most complicated as well as one & or by the most simple means: to give one instance:—in many diœcious plants pollen is carried from the

(48

(48

male to the female by the wind, which is perhaps the simplest method conceivable, or by the adherence of on the grains to the hairy bodies of insects, which is a method only a little less simple; or, by the but as in Catasetum the conveyance must then most is effected by the most complex machinery; for in this orchid we have sensitive horns causing which when touched cause a membrane to rupture, & setting this sets free certain springs by which the pollen-masses are shot forth like an arrow, which adhere & they adhere to the insect's body by a peculiar viscid matter, & then by the breaking of an elastic thread of cal the right strength the pollen is left gl sticking to the stigma of the female plant. The complexity of the means sometimes used by nature to gain a certain end purpose, in this & in many other cases, in fact depends on all the previous stages through which the species has passed, & on the successive adaptations of each part during each stage to changing changed conditions of life.)

(As some authors seem to apparently consider that dimorphism means as to be the first stage to a step toward diœciousness      should be observed how difficult that it is diœciousness condition, it may be well to remark that it is difficult to imagine to imagine by which steps diœciousness the difficulty of understanding how how

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(49

by what gradual steps how a trimorphic species plant, like Lythrum salicaria could become diœcious should be noticed; & consequently; & as dimorphism & trimorphism seem are so closely allied, in nature that I do not believe that dimorphism is it is not probable that either state is aboriginally necessarily in any way in any way related to a dioecious condition; separation of the sexes: but though, as I hope on to show on a future occasion to show that apparently it does does sometimes pass into its lead to a separation of the sexes. it may occasionally lead to this end. As far as Lythrum salicaria is concerned, the one tendency which we see can discover is towards the condition of which we have the abortion of the two sets of male organs stamens in the mid-styled form. & The This tendency being is evinced shown only shown merely in the at by its pollen, though abundant & apparently good, yielding a smaller percentage of seed than does the pollen of the corresponding stamens in the other two forms; & this fact therefore is in itself curious, & shows by what insensibly graduated steps nature moves. If this tendency were carried out we should have the mid-styled form would become a female, depending for its fertilisation on two sets of stamens in the long- and short-styled forms; & these two forms would reciprocally

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(50

fertilise each other like the two forms of Primula or Linum; but we shd be no nearer diœciousness.)

Before (As the case of the trimorphic species of Lythrum salicaria is so complicated, & as it is sometimes perhaps easier to perceive appreciate understand the relations of the sexes in the animal kingdom than in the vegetable kingdom, it may be worth while to give, before concluding, a somewhat elaborate simile. We may take the case of a species of ant, & we must then suppose that all all the individuals invariably to live kind in three kinds of communities; in the first, we [illeg] should been a large-bodied sized female (not to specify other differences) living with six mid middle-bodied sized & six small-sized males; in the second community a middle-sized female with the same number of would live with six large- & six small-sized males; & in the third community, a small-sized female would live with six large- & six middle-sized males. Each one of these three females, though she could enabled to unite with any male, would be ster nearly sterile with ten her own the two sets of males, living with her,

(51

(51

& likewise with two other sets of males living in in the other two communities; for she would be fully fertile only when paired with a male of her own size. [illeg] (a) from one living in either of the two other communities. We should moreover find that the two sets of males living in the community of the big extraordinarily fertile middle-sized community was less female would be sexually potent potent sexually than the males of corresponding size it is inhabitants that inhabitants in the two other communities. Lastly we should find that from from the eggs laid by all each of the three females, all three sorts of the these females & all three sorts of males were repeatedly habitually reared; proving to demonstration that all belonged to one & the the same species.)

(To appreciate fully the case of the reciprocally trimorphic species of Lythrum, we may take a glance at the two great kingdoms of nature & search for anything analogous. to With animals we have the most astonishing diversity of structure during their development

[51v]

(a)

Hence the thirty-six males, distributed by half-dozens in the three communities, would be divided into three sets of a dozen each; & these sets, as well as the three females, would differ from each other sexually, in exactly the same manner as so the do distinct species of the same genus. Moreover the two

(52

(52

in the so-called cases of alternate generation, but as such animals have not arrived at maturity, they are not properly comparable with the forms of Lythrum. With mature animals we have extreme differences in structure in the two sexes; we have the same species some of the lower animals existing males, females, & hermaphrodites; we have the somewhat more singular curious case of certain hermaphrodite cirripedes which are hermaphrodites, but are sexually aided by a whole clusters of what I have called complemental males; we have, as Mr. Wallace has lately shown, the females of certain Lepidoptera existing under three distinct forms; but in none of these cases is there any reason to suppose suspect that there is more than one female or one male sexual element. With certain insects, as low as with ants in which there exist besides males & females, two or three castes of workers, we have a slightly nearer approach to our case, for the workers are so far sexually affected, as to have been rendered sterile. With plants, at least with phanerogamic plants, we do have not

(53

(53

that wonderful series of changes during successive forms developmental development forms, so common with animals; nor could this be expected, as the plants are fixed to one spot from their birth & must be exposed subject adapted throughout life to the same conditions. With plants we have not such marked sexual differences; nor could this be expected as sexual.

With plants we have sexual differences in structure, but apparently less strongly marked than with animals, the from causes of which in part was are plainly intelligible, such as there being no sexual selection; again we have that class of minute, imperfectly developed & self-fertile flowers, lately so ably dimorphic dimorphic flowers, so ably discus sed by Hugo von Mohl Mohl, in which part of the some flowers some of the flowers are minute, imperfectly developed, & necessarily self-fertile, whilst others are perfect & are capable of crosses at least capable of crossing with other flowers according to their [illeg] class & at least capable of crossing with other of the same species; but in these several cases we have no reason to supposed suspect that there is more than one female or one male sexual element. When When we come to the class of called by me reciprocally dimorphic flowers, we search any occur plants, such as

(54

(54

in Primula, Linum, &c, we first meet with two male & two female masculine & two feminine sexes. But these cases which seemed but the other yesterday day only a short time since so strange, sink now sink almost into insignificance before that of the trimorphic species condition trimorphic species of Lythrum.) (Naturalists are so much accustomed to the behold great diversities of structure associated with the two sexes, that they feel no surprize at the fact; but differences in the sexual elements nature have been thought to be the very touchstone of specific distinction.

We now see that such sexual differences—the greater or lesser power of fertilising or being fertilised,—may characterise & keep separate the co-existing individuals of the same species, in the same manner as they characterise & keep have kept separate those groups of individuals, which have been produced from common parents during the lapse of ages & so or in different regions, which we rank and denominate as a distinct species.)


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Citation: John van Wyhe, ed. 2002-. The Complete Work of Charles Darwin Online. (http://darwin-online.org.uk/)

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