144 MEANS OF DISPERSAL. [Chap. XH 



conclude, as far 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 retain their power of germination. In 

 Johnston's Physical Atlas, the average rate of the sev- 

 eral Atlantic currents is 33 miles per diem (some cur- 

 rents running at the rate of 60 miles per diem); on this 

 average, the seeds of ^-g plants belonging to one coun- 

 try 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; 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 flota- 

 tion and their resistance to the injurious action of the 

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

 dry the 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 -^ 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 ^\ 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 



