OCEANIC DISPERSAL OF PLANTS. 283 



To test still further the kinds of seeds which appeared sound in the first experiment, 

 thirty-four of them were subjected to a trial of ninety-three days' duration. Only nine 

 of them withstood this trial and germinated, when placed under the most favourable con- 

 ditions, namely : Cucurbita pepo, Acacia julibrissin, Xanthium macrocarpum, Beta vul- 

 garis, Rumex aquations, Ricinus africanus, Ricinus communis, 1 Ephedra distachya, and 

 Carina gigantea. And of these the Acacia and Canna do not float, 2 so that out of a total 

 of ninety-eight kinds, only seven 3 retained their germinative power after three months 

 floating on the sea. This, as Martins observes, is a very small proportion, and then the 

 chances of their germinating and establishing themselves if cast ashore are infinitesimally 

 small ; yet it does not follow, we think, that the sea has exercised a comparatively in- 

 appreciable influence in the diffusion of the vegetation of the world, though the number of 

 species so transported be relatively insignificant. 



A third series of experiments, with the same object, was undertaken by Mr Gustave 

 Thuret, at the instigation of M. Alphonse De Candolle. The results 4 were much the 

 same as those obtained by Martins ; but as the seeds were subjected to a thirteen months' 

 ordeal, it is interesting to note the species that survived and germinated afterwards. They 

 were : Silene atocion, Hibiscus speciosus, Medicago sativa, Mesembryanthemu m crystal- 

 linum, Apium graveolens, Cichoriwm endivia, Campanula laciniata, Lycopersicum 

 esculentmn, Phytolacca sp., and Beta vulgaris. From the prolonged period these seeds 

 withstood the action of sea- water it would seem that certain seeds are practically imperish- 

 able therein ; and, what is more remarkable, Mr Thuret states that several of them not 

 only germinated, but actually grew more vigorously than corresponding samples of the 

 same seed kept dry during the same period. It is noteworthy, too, that the ten plants 

 which underwent this trial, belong to as many different natural orders ; and they are not 

 specially maritime plants. Doubtless the condition of the seed at the time of immersion 

 has much to do with its capability of floating, and likewise of its power of enduring the 

 action of sea-water. In a note at the end of Thuret's paper De Candolle reiterates his 

 conviction that oceanic currents exercise extremely little influence in the diffusion of 

 plants, and that it is limited to the littoral element. Thuret 5 himself is more dogmatic, 

 for he says, with the exception of plants that grow naturally on sandy or muddy sea-shores, 

 one could not seriously admit that seeds stranded on the sea-shore would ever find 

 the conditions necessary for their development and the propagation of their species. 



Without actual proof of the contrary, this might be treated as a false inference, 

 because we know that many plants, not specially littoral, grow equally well just above 

 the ordinary high-water line as farther inland ; and in stormy weather, the only times at 



1 Varieties of one species. 



2 The pods of the former probably would. 



3 Only six, counting the varieties of Ricinus as one. 



4 Archives des Sciences de la Bibliotheque Universelle, July 1873, p. 177. 



5 Loc. cit., p. 182. 



