Distribution of the Laminariacem. 367 



the northern snbtribes are to the northern hemisphere. The Macro- 

 cystese have the most extended range as far as latitude is concerned, 

 extending from the southern point of South America to the north- 

 western corner of North America. In the case of the other sub- 

 tribes the distribution is not so continuous. The Ecklonese have pos- 

 session of Australia and Cape Horn, but reappear in peculiar forms 

 in California and Japan. The Lessonese extend up the western 

 coast of North America and reappear on the western coast of North 

 America in forms peculiar to that region. 



Arguing from the fact that certain species of algse are practically 

 cosmopolitan, being found in almost all marine waters, we may 

 readily believe that if an alga be of such constitution as to endure 

 almost any condition of heat or cold, freshness or salinity, etc., 

 which may be found in the ocean; such a species would be found 

 almost everywhere. Consequently we may also believe that a more 

 or less limited distribution means that the particular form is unable 

 to endure certain conditions found along the borders of the area 

 inhabited by it and that thus barriers are raised against its farther 

 dispersion. Within a particular area, a species is dispersed b}' the 

 various tides, currents, swells, etc. of the waters of that area. 

 Apropos of this subject Hooker has said:^ "We are accustomed to 

 regard the ocean as so ever-active and powerful an agent in facilita- 

 ting migration, and its uniform temperature is so conducive to the 

 general diffusion of species, that it seems almost wonderful that 

 Algm should have limits to their distribution, especially in waters 

 which gird the globe on the same parallel of latitude, and whose 

 unchecked swells and currents literally extend over every degree of 

 longitude." 



The temperature of the water has perhaps as much to do, as any 

 one thing, in limiting the distribution, and yet this is not the only 

 thing. Species may be carried across even fairly wide areas of 

 water whose temperature is unfavorable to their growth, by currents 

 passing from the areas which they inhabit. Hooker goes on to say: 

 " The remarkable increase in temperature of the tropical over the 

 polar seas of the Atlantic may, and probably alone does, check the 

 progress of the Macrocystis in its course from Cape Horn to the 

 equator in that ocean, for, . . . the same sea-weed can float with 

 the colder currents of the Pacific from the same Cape to Behring's 

 Straits ; but no such obstacle prevents the fullest interchange of 



' Flora Antarctica, Pt. 2, p. 467. 



