OCEANIC DISPERSAL OF PLANTS. 281 



vitality. In this he was assisted by Sir Joseph Hooker, and the Rev. M. J. Berkeley con- 

 ducted a similar set of experiments, the results of which first appeared separately in the 

 Gardener's Chronicle, afterwards jointly with Darwin's in the Journal of the Linnean 

 Society. The principal fact ascertained from these experiments was that the seeds of 

 many plants belonging to the most widely different natural orders germinated after long 

 immersion in sea-water — some after upwards of 100 days ; and these were not by any 

 means all seeds of plants which naturally inhabit the sea-shore or salt marshes ; yet among 

 them were Atriplex, Beta, Spinacia, and Rheum. A species of Capsicum endured the 

 trial best, thirty seeds out of fifty-six having germinated well after 137 days' immersion. 

 But Darwin was led to believe from these experiments that he had previously over-esti- 

 mated the action of the sea on the dispersion of plants, for he says : — " I soon became 

 aware that most seeds, in accordance with the common experience of gardeners, sink in 

 water ; at least I have found this to be the case, after a few days, with the fifty-one kinds 

 of seeds which I have myself tried ; so that such seeds could not possibly be transported 

 by sea-currents beyond a very short distance. Some few seeds, however, do float, as I 

 have tried with some of those cast by the Gulf Stream on the coast of Norway. From 

 knowing that timber is often cast on the shores of oceanic islands, far from the mainland, 

 and from having met with accounts of floating vegetable rubbish off estuaries, I assumed 

 that plants, with ripe seeds, washed into the sea by rivers, landslips, &c, might be drifted 

 by sea-currents during a period of some weeks. The closing of capsules, of pods, and of 

 the heads of Composite, &c, when wetted, and their re-opening when cast on shore and 

 dried, the seeds being thus allowed to be driven inland by the first stormy winds, seemed 

 to favour such means of transport. But in putting thirty-four plants of different orders, 

 with ripe fruit, into salt water, one alone (Euonymus) floated a month, being buoyed up 

 by its fruit ; the others all sank in twenty-one days, some in five, and several in seven, 

 nine, and eleven days. But I am not sure that I have made the trial fairly, for I kept 

 the floating plants in too warm and dark a place, which might have favoured their 

 decay." 



Of course, Darwin's experiments proved nothing of any plants not tried, and not 

 everything bearing on the question of those that were tried. Thus, the seed-vessels, 

 enclosing seeds, of some of them might float, though on looking through the list very few 

 of the species are such as are likely to be conveyed from place to place by the sea, except 

 under extraordinary circumstances. Subsequently Darwin made some more experiments, 

 and he found that many things which sank when green, or floated only a short time, 

 floated a long time when dry. 1 Thus, ripe hazel-nuts sank immediately, but when dried 

 they floated for ninety days, and afterwards when planted they germinated. An aspa- 

 ragus plant with ripe berries floated for twenty-three, when dried it floated for eighty-five 

 days, and the seeds afterwards germinated. Ripe seeds of Helosciadium sank in two 



1 Origin of Species, p. 359. 



p Of 



(BOT. CHALL. EXP. — PART III. — 1885.) ° 



