144 MEANS OF DISPERSAL. [Chap. XII. 



as anything can be inferred from these scanty facts, that 

 the seeds of -^^ kinds of plants of any country might be 

 floated by sea-currents during 28 days, and would re- 

 tain their power of germination. In Johnston's Physical 

 Atlas, the average rate of the several Atlantic currents 

 is 33 miles per diem (some currents running at the rate 

 of 60 miles per diem) ; on this average, the seeds of j^^ 

 plants belonging to one country might be floated across 

 924 miles of sea to another country, and when stranded, 

 if blown by an inland gale to a favourable spot, would 

 germinate. 



Subsequently to my experiments, M. 'Martens tried 

 similar ones, but in a much better manner, for he placed 

 the seeds in a box in the actual sea, so that they were 

 alternately wet and exposed to the air like really float- 

 ing plants. He tried 98 seeds, mostly different from 

 mine J but he chose many large fruits and likewise 

 seeds from plants which live near the sea; and this 

 would have favoured both the average length of their 

 flotation and their resistance to the injurious action of 

 the salt-water. On the other hand, he did not pre- 

 viously dry tlie plants or branches with the fruit ; and 

 this, as we have seen, would have caused some of them 

 to have floated much longer. The result was that ^f of 

 his seeds of different kinds floated for 42 days, and were 

 then capable of germination. But I do not doubt that 

 plants exposed to the waves would float for a less time 

 than those protected from violent movement as in our 

 experiments. Therefore it would perhaps be safer to 

 assume that the seeds of about j\fj plants of a flora, 

 after having been dried, could be floated across a space 

 of sea 900 miles in width, and would then germinate. 

 The fact of the larger fruits often floating longer than 



