432 A NATURALIST IN THE PACIFIC chap. 



currents in temperate regions is of some importance, and Sernander 

 arrived at a similar conclusion when discussing the origin of the 

 Scandinavian flora. The few plants with buoyant seeds and fruits, 

 such as Arenaria peploides, Cakile maritima, Crithmum maritimum, 

 Convolvulus soldanella, Euphorbia paralias, and Lathyrus mariti- 

 mus, are no doubt thus dispersed, and Norman is quite right in 

 attaching some value to the distribution by currents of certain 

 plants within the region of the Arctic flora ; but after all it amounts 

 to little, and geographical and climatic conditions have often had 

 a predominant influence in determining the distribution in the 

 temperate latitudes of littoral plants possessing buoyant seeds or 

 fruits. 



Nowhere is this shown more plainly than with the littoral plants 

 with buoyant seeds or seed-vessels that are found on our English 

 beaches. Some have evidently acquired their present distribution 

 before ice and snow reigned supreme in the extreme north. Though 

 it may be possible, it seems highly improbable, that either Arenaria 

 peploides or Lathyrus maritimus, both of which occur on beaches 

 in high northern latitudes in the Atlantic and Pacific Oceans (as in 

 Arctic Norway, Spitzbergen, and Behring's Straits), could possess 

 in our own day any means of communication between their areas 

 of distribution on the borders of these two ocean-basins. 



So again with Cakile maritima, the occurrence of this or of two 

 closely allied species on both sides of North America cannot be 

 attributed to any present working of the currents for two reasons. 

 In the first place, as is remarked in Note 18, the results of two 

 independent experiments made by me show that the fruits will not 

 float more than a week or ten days in the sea, a capacity that will 

 not admit of their transportation by the currents over tracts of 

 ocean more than one or two hundred miles across. In the second 

 place, this species is not an Arctic plant like Arenaria peploides 

 and Lathyrus maritimus ; and the possibility of inter-communica- 

 tion between the Atlantic and Pacific Oceans having any effective 

 value from the standpoint of dispersal, shadowy as it is with the 

 two Arctic species, is still more so in the case of Cakile maritima. 

 Norman's observations on the coast of Norway, as quoted by 

 Sernander (page 123), indirectly indicate how hopeless it would be 

 for this plant to attempt to traverse the Arctic region. Just as I 

 have noticed on the north coast of Devonshire, the fruits occur 

 plentifully in the beach drift and germinate freely in the upcast 

 wrack as far north as Senjen in latitude 6g°. Further north the 

 plant has been recorded from only eight localities, and since it is 



