RECORD: Darwin, C. R. & Francis Darwin. [1878]. Draft letter to an American periodical on Thalia dealbata / Draft of Cross and self fertilisation, folios 693, 724, * (3) pages 86 and 725. CUL-DAR209.13.19-22. Edited by John van Wyhe (Darwin Online, http://darwin-online.org.uk/)

REVISION HISTORY: Transcribed by Christine Chua and edited by John van Wyhe 7.2023. RN1

NOTE: See record in the Darwin Online manuscript catalogue, enter its Identifier here. Reproduced with permission of the Syndics of Cambridge University Library and William Huxley Darwin. The volume CUL-DAR209.13 contains materials on fertilisation (Thalia) for Darwin's book Movement in plants (1880). Draft in the hand of Ebenezer Norman with corrections by Darwin. The text of the draft corresponds to Cross and self fertilisation, pp. 400-401, 403, 420-21 and 421.


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[ July 1878]

I beg leave hope to call if you will permit me through your columns the attention of any the Bot in who lives in the S. U States & who is interested in the filaments of flowers to those of Thalia dealbata. They present, as far as I know a unique peculiarity, in action, which I have not been able am n not able fully to investigate comprehend. They flo stand as pair, & the right side of one converge converged in [illeg] with left side of the [illeg]  flower & so with in [2 words illeg] opened side. They occur in pairs, & Each flow is so far very simple that it include only a single stamen & pistil, but in the shape of its petals the perianth (I believe modified stem) it possesses an petal-like organs it is a complex in structure as an orchid. It The pistil in its growth growing

[remainder of  the draft not transcribed]

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693 82

Chap. _ E 10

as ferns, possessed both sexual organs there can hardly be a doubt; and this shows, as Hildebrand remarks,* 2 (*2 Die Geschlechter_Vertheilung. 1867. p. 84-90), at how early a period the sexes were separated. As soon as plants became phanerogamic and grew on the dry ground, if they were ever to intercross, it would be indispensable that the male fertilising element should be transported by some means through the air; and the wind is the simplest means of transport. Moreover there must also have been a period when winged insects did not exist, and plants would not then have been rendered entomophilous. Even at a somewhat later period the more specialised orders of the Hymenoptera (201), Lepidoptera, and Diptera, which are now chiefly concerned with the transport of pollen, did not exist.

Therefore the earliest terrestrial plants known to us, namely, the Coniferæ and Cycadiæ, no doubt were anemophilous, like the existing species of these same groups. A vestige of this early state of things is shown by some

[2]

In a young unopened flower the pistil was straight, with the cavity concavity on its crown already charged with pollen. Beneath the concavity there is deep hollow, which appears to be the stigmatic surface, & again beneath a large, rigid, dependent membrane curtain. When the flower is mature this curtain stretches partially across the passage down the flower, & wd be pushed by any insect try to enter it.

The lower part of the pistil by a curvy shaped petaloid body, which is prolonged into two long solid tapering nectaries, which stretch transverse across the outer side of the flower, & which secrete an abundance of nectar.

At the base of one of the 2 nectaries there is a little white smooth hook, which seems to retain the pistil in its straight uncoiled & upright position; but I am doubtful on this head, for the pistil after it has suddenly assumed its spiral shape is [extraordinarily] rigid & cannot be again straighten, & it appears impossible that any petal shd be strong enough to retain it, unless indeed its rigidity is assumed acquired

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* (3) page 86

I published a brief notice of this case in the Gard. Chronicle, 1855, July 21 p. 487, and afterwards made some further observations. Besides the hive-bee, another species of bee, a moth, ants and two kinds of flies sucked the drops of fluid on the stipules; the larger drops which when large tasted sweet. The hive-bees never even looked at the flowers which were open at the same time; whilst two species of humble-bees neglected the stipules and visited only the flowers.

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as soon as it becomes spiral. I could do not make out certainly what part believe that any part of the flower is sensitive, but that like the teeth of a rat-trap, the pistil is held in such a manner it acts like that a very delicate touch liberates it. like I dropped

A flower was dropped accidentally on the stage of the [illeg], from a height of only about half an inch, & this set the pistil free: on two occasions touch pressing light slightly the light pressure on the transverse curtain lightly with the a thin bristle acted as far as I could judge: on another occasion I moved the tips of the nectaries several time with no result, but on doing so in another flower, the pistil instantly shot out.— Judging from the state of old half-withered flowers, the pistil ultimately liberates itself without any aid; & as the pollen in the concavity on the summit is separated from the stigmatic cavity only by a knife-edge, I can hardly doubt self-fertilisation follows from the opening of the pistil: in this respect Thalia resembles Corydalis ... If Therefore a bee with a clean proboscis visits a flower it will cause self-fertilisation, but will carry away pollen, & if it then visits another flower on a distinct plant

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724 (10

Ch XI

by visiting flowers only a few of the petals lost that the calyxes alone flowers without any petals were still worth visiting by finding nectar in those with only some of their petals lost.

The colour of the corolla  serves as an approximate guide: thus I watched for some time humble-bees which were are timed their visits visiting exclusively plants of the white-flowered spiranthes autumnalis, growing on short turf at a considerable distance apart; and these bees often flew within a few inches of any several other plants with white flowers, and then without further examination passed onwards in their search of the Spiranthes. Again, I saw many hive-bees which confined their visits to the common ling (Calluna vulgaris), repeatedly flew towards Erica tetralix, evidently attracted by the nearly similar colour tint of their flowers, and then instantly passed on in search of the Calluna.)

That the colour of the flower is not the sole guide by is clearly shown by the five cases above given, of bees which repeatedly travelling passed in a direct line from one variety to variety another of the same species,

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it will render cross-fertilisation in a high degree probable. As far as I could judge as soon as the pistil has once become spiral the stigma will not be touched by an insect — In this respect & in the sudden movement of the pistil Thalia presents some analogy with a widely different plant, namely Corydalis ... But all these points require further investigation, & especially the mechanism by which pistil is prevented from coiling itself int a spire until some part of the flower is touched.— : I have rarely ex & rarely seen a more sin curious phenomenon, than the instantaneous coiling of the pistil, & the sight will reward anyone who has an opportunity of making more careful observations than mine.—

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725 (11

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which had although these bore very differently coloured flowers, Again I observed also bees passing flying in a straight line from one clump of a yellow-flowered Oenothera to every other clump of the same plant in the garden, without turning an inch from their course to that plants of Eschscholtzia and others with yellow flowers which lay only a foot or two on either side. In these cases the bees knew perfectly well, as we may judge infer by the directness of their courses flight the position of each flower plant in the garden; so that they were guided by experience & memory. But how did they discover at first that the above varieties belonged to the same species? Improbable as it may appear, they seem, at least sometimes to recognise plants even from a distance by their general aspect in the same manner as we should do.

On three occasions I observed humble-bees flying in a perfectly straight line from a tall larkspur (Delphinium) which was in full flower to another plant of the same species at the distance of fifteen yards which had not as yet a single flower open, and on which the buds showed only a faint tinge


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