436 GENERAL MORPHOLOGY OF PLANTS 



and Asia, there are at present evidences of this migration of 

 plants southward. Many arctic plants which at that time moved 

 southward are now left on the higher mountain peaks, or in the 

 cool sphagnum moors formed among some of the terminal 

 moraines. With the proximity of the continents in the arctic 

 circle there is reason to believe that in former times plants 

 migrated readily between the continents of North America, 

 Europe and Asia. During glacial times these were forced 

 southward, in Europe, North America and Japan. Evidence of 

 this is shown in the close relationship of the flora of northern 

 Europe, North America and Japan. Many species and genera of 

 plants found in these countries are the same. Under the present 

 conditions of the climatology of the earth it would be impossible 

 for the plants to communicate to such an extent as to explain 

 the presence in these different continents of such a large number 

 of the same species. While in the seed plants there are many 

 similarities in the flora, and many species and genera are iden- 

 tical, in the lower forms, among the algae, fungi, liverworts and 

 mosses, there is an even greater similarity. This leads us to 

 believe that even microscopic plants like the fungi and algae 

 migrated under these conditions along with the seed plants. The 

 parasitic fungi moved along with their hosts, and saprophytic 

 fungi, like the mushrooms, followed the movements of forest 

 trees, growing on dying or dead trunks, upon the leaves, and 

 leaf-mold in the forest. The aquatic fungi and the fresh-water 

 algae likewise moved southward with the aquatic flowering plants. 

 The fact that so many of the fresh-water forms of the fungi and 

 algae, as well as of the flowering plants, are identical with many 

 of those in northern Europe suggests that in former times the 

 continents in the arctic circle were very near together, if not act- 

 ually connected, that the climate was milder, and that there was 

 a migration of these fresh-water plants between the continents. 

 This might be brought about by a possible continuity of land and 

 fresh-water areas; or through the migration of water-fowl the 

 spores of algae and fungi clinging to their feet could be trans- 

 ported across land areas or channels of salt water, when these 



