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On the action of sea-water on the germination of Seeds, by Charles Darwin, Vice Pres. R. S.— F.L.S.—

During the spring of last year it occurred to me that it would be worth while, in reaction relation to the distribution of plants, to test how long seeds could endure immersion in sea-water, & yet retain their vitality. As far as I then knew this had not been tried by botanists, who would have been far more capable of doing it efficiently than myself; & I now find that M. A. de Candolle, in his admirable work on Geographie Botanique, regrets that such experiments have not been tried; & I think, that had he known even the few facts here to be recorded, some of his opinions on the means of distribution of particular families would have been slightly modified. The Rev. J. M. M. J. Berkeley has likewise tried tested 53 different kinds of seeds & has published a report in the Gardeners Chronicle*, li to which periodical I have, also published sent two brief notices on the same subject†. I intend here to give, with Mr. Berkeley's kind permission, an account of our joint experiments. I may premise, that not knowing, at first, whether the seeds would endure even a

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* Sept 1st 1855 nor 35

† May 26th and Nov. 24th, 1855.

o Salting Seeds / Floating Plants / 12.

on Salting Seeds / (1 x 6r) 12.

// 46 //

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week's immersion, I selected them a few by simple chance, taking however the seeds of different families; subsequently I have been aided by suggestions from Dr. Hooker.

I must briefly describe how my experiments were tried: the seeds were placed in small bottles, each holding 2 or 3 ounces of salt-water, carefully made according to Schweitzer's analysis: as both algæ & marine animals have, as is well known, long survived in water thus made, there can be no doubt that that the experiment has been was thus fairly tried. Mr. Berkeley sent his seeds to Ramsgate, tied up in little bags & placed in real the sea-water, daily renewed; & they were thus immersed for three weeks, & when partially dried dried, but but still damp, were sent off, but by accident were not unpacked for four days subsequently, so that their total immersion "was equivalent to one of more than a month." Some of my bottles were put out of doors in the shade, & were exposed to an average weekly temperature an average of from 35° to 57°: the other bottles were kept in my cellar & were exposed to much less variation of temperature, viz from weekly daily mean average of 46° to 56°. Further, to test the effect of temperature, I immersed immersed 18 different sorts of seeds in little bags in salt water, in a tank, which from containing much snow, was for 6 weeks was at the temperature of 32°, slowly rising for the next six weeks slowly rise to 44°; but the seeds thus tested did not seem

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to withstand the injurious effect of the salt water better than those exposed to the above specified considerable variations of a higher but variable temperature. I may remark that amongst the 18 kinds of seeds immersed in the cold salt-water, there were seeds of a somewhat tender capsicum & vegetable marrow, but the exposure to the cold in no degree injured their germination. In the case of some of the seeds which I first tried first, & which were put out of doors, I did not change the salt-water for the first 56 days, & it became putrid & smelt offensively to a quite surprising degree, especially the water with the cabbage, radish, cress & onion seed, which also gave out strongly the odour of each kind; so that I thought the putridity it would infallibly have caused the putrefaction of been communicated to the seeds; but, judging from the seeds of some of the same plants (but not actually of from the same lot of seed) placed in salt-water often renewed, & likewise kept in the cellar under a less variable temperature, neither the putridity of the water nor the changing temperature had much any marked effect on their vitality. Seeds of cress Cress seed (Lepidium sativum) & that of Phalaris canariensis, after 22 days immersion were thoroughly dried for a week & then planted; they germinated pretty well, but the seeds themselves of this particular lot were not very good. At first I tried

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some of the seeds, after each successive week's immersion, & it was surprising to see they germinated at the same in less same period after being planted, with as did seeds of the same kind which had not been salted; celery & rhubarb seed, however, were somewhat accelerated in their germination. Some kinds of seed, as of Trifolium incarnatum, Sinapis nigra, Peas, kidney & common Beans, swelled much in the salt-water, & they generally had germinated were killed by a short immersion; but the swollen seeds of Lupinus polyphyllus germinated better than those which did not swell. I was surprised to observe that most of the seeds of Convolvulus tricolor germinated after seven days under the salt-water & lived for some time in it; as did likewise the fresh seed of Tussilago farfara after 9 days; after 25 days I took out some of the young plants of the latter Tussilago & planted them, & one of them grew: some of the seeds of the garden Atriplex orache (Atriplex) also germinated under water after 56 days immersion, but I failed in raising the seedlings; the other seeds of the orache same lot of or of the orache germinated excellently after 100 days immersion.—

The total number of seeds tried by Mr. Berkeley & myself amount only to 87, for unfortunately we happened to select some of the same kind; in one respect, however, this has been fortunate, for we have thus tested each other's results, & they accord perfectly as far as they go; the seed of the Tomato, however,

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germinated better after a month immersion with Mr. Berkeley than with me after only 22 days with me; but my seed l appeared to be old. And this leads me to remark, that I suspect that fresh seed withstands the salt-water better than old, but yet very good seed; this certainly was the case with Trifolium incarnatum, Phlox Drummondii & I believe with Sinapis nigra. Of the same genus Godetia, Mr. Berkeley found one species was killed & another survived to survived a month's immersion: but a far more curious case is presented by the varieties of the cabbage; there for I found that good seed of the "Mammoth white Broccoli" germinated after 11 days immersion, but was killed by 22 days; seed of the "Early Cauliflower" survived 22 days; but was killed by 36 days; "Cattell's cabbage" germinated excellently after 36 days, but was killed by 50 days; & lastly fresh seed of the wild cabbage from Tenby germinated excellently after 50 days, very well after 110 days, & two seeds out of some hundreds germinated after 133 days' immersion.

Of the 87 kinds of seeds tried, 23 or more than one quarter did not endure 28 days immersion: capsicum has endured the trial best, for 30 out of 56 seeds germinated well after 137 days immersion: of celery seed after the same period of 137 days, only 6 out of several hundreds germinated. The

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worst germinators have been dwarf kidney Bean, & Hibiscus manihot, both killed by 11 days immersion; the common Peas were killed by 14 days; Tussilago farfara germinated under water after 9 days, but the young plants kept alive for some time: the next worse germinators have been Phlox Drummondii, Trifolium incarnatum, Linum usitatissimum & Sinapis nigra, very few of only of which survived 15 days.

We may perhaps infer from this that but few seeds, would especially fresh seeds, would.

From such scanty materials it is, perhaps, rash to draw any sort of deduction in regard to the power of resistance to salt water in the different divisions of the vegetable kingdom; but a few remarks may be admirable permitted. only 3 Three out of the 17 endogens were killed by a months immersion, whereas and 20 out of the 70 exogens were killed by a months or 28 days immersion; of the this fact, together with the marked power of endurance in the Atriplex, Beta, Spinacea & Rheum, lowly organized exogens, accords with, & is perhaps connected with, the fact insisted on so much by A. Decandolle, of the wider range of the species Endogens, & of the lowly organized exogens, than of the other higher exogens.

The four Solanaceæ & two Umbelliferæ endured the salt-water very well, & each included the longest survivor of all the species tried. Ten Compositæ were

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tried, & only was one was killed by a months immersion, besides that is excepting the Tussilago which germinated under water. Eight Cruciferæ were tried, & all withstood the influence well, excepting Sinapis nigra, which was killed by 25 days' immersion: three of the Cruciferæ then survived 85 days: this power of endurance in the Cruciferæ perhaps, surprising considering the oil in their seeds.—

Nine Leguminosæ were tried; these all resisted the salt-water badly, with the exception of the hard thin seeds of Mimosa sensitiva, which germinated pretty well after 50 days; three species of Lupine seemed just able occasionally to withstand about 36 days immersion; the seeds of the others seeds Leguminosæ (a) Back of Page having all been killed by much shorter periods.

Lastly, seven species of the allied families of Hydrophyllaceæ & Polemoniaceæ. and all, (six (six having been selected by Mr. Berkeley) as observed by Mr Berkeley, all were killed by a month's immersion; & the Phlox & so great a proportion cannot have been can hardly be accidental.

I had intended trying many more seeds, as I at one time thought they that these experiments would have thrown more light on the dispersal of plants than I now think they do. I soon became aware that most seeds, in accordance with the common experience of gardeners, sink after in water; at least I have found this to be the case, after a few days, with the 51 one kinds of seeds, which I have myself tried; so that such naked seeds could not possibly be transported by sea-currents beyond a very short distance. as soaked seeds, except possibly along the bottom of shallow seas, [illeg] the

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(a) (text)

I suspect that it is the water, & not the salt, which kills the Leguminosæ, at least I found that a lot lot of fresh "Thurston Reliance" Peas were all killed by 13 days immersion in plain pure water: & I have been assured that a much shorter time immersion will kill Kidney Beans.—

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B[illeg] Some few seeds, however, do float, as I have tried with some of those cast by the Gulf-stream on the coast of Norway. But From knowing that timber is often cast on the shores of oceanic islands far from the mainland, & from having met with accounts of floating vegetable rubbish at sea off estuaries, I assumed that plants, with the ripe seeds, washed into the sea by rivers, landslips, &c, as as would might be drifted by an oceanic  sea-currents during a period of some weeks. The closing of the capsules, pods, & heads of the compositæ &c., when wetted, & their reopening when cast on shore & dried, as could happen happen when cast on shore & & thus allowing them to be driven a little inland by the first stormy winds, seemed to favour such means of transportal. But in trying putting 34 plants of different orders, with ripe fruit, into salt- water, one only alone, the l Euonymus, floated for a month, being buoyed up by its fruit; the others all sunk in 21 days, some in 5 & several in 7, 9, & 11 days. But I am not sure that I have tried this fairly, for I kept the floating plants in too warm & dark their a place, which might have favoured their decay. Finally I may remark that all the seeds of very few species are, as far as we yet know, all killed by 10 days immersion,—that some plants

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will float for this period,—that the average rate of the ten currents in the Atlantic Ocean, given in Johnston's Physical Atlas, is 33 miles per diem (the main Equatorial current running at the rate of 60 miles, & the Cape Stream at 80 miles per diem); & therefore I conclude, under the existing extremely scanty materials for forming any opinion, that some species plants might occasionally under favourable conditions be transported over arms of the sea 300 300, or even more miles in width breadth; & if cast on sh the shore of an island not well stocked with plants species, might become naturalised.

(The following had better not be read to the Society)

In the following list, to save repetition, I have marked the plants tried by Mr. Berkeley, & which germinated after a month's immersion, with (+) in brackets ; when they did not germinate, this is expressly stated. The "cold water" refers to the seeds placed in salt- water in the tank with snow.

I have grouped together the species which belonged to the same great natural families, & have left the others unarranged, merely separating the Exogens & Endogens.—

I have arranged the Families in accordance with Lindley Vegetable Kingdom.—