GEOLOGICAL AND GEOGRAPHICAL DISTRIBUTION 543 



The writer recalls vividly the strangely familiar aspect of the 

 vegetation of Japan, especially in the island of Yezo, where nearly 

 all the more conspicuous plants were either the same, or closely 

 related to common species of the Atlantic states. Such character- 

 istic plants as the Fox-grape, Poison-ivy, Sumach, Bittersweet 

 (Celastrus), Sensitive-fern (Onoclea seiisibilis), Elms, Maples, Beeches, 

 Oaks, and Magnolias, all closely resembling or identical with Eastern 

 American species, were striking features of the vegetation. "\Vere 

 these forms also common to our Pacific coast, and extended across 

 the continent, there would be nothing remarkable in encountering 

 them in Japan, but most of them are quite wanting in the Pacific 

 states and the intervening country. 



Professor Asa Gray made a very careful study of the relation of 

 the Japanese flora to that of North America, and states that over 

 60 per cent of the Japanese plants are represented in our Atlantic 

 states by either identical species or closely related ones. This is 

 against 37 per cent for Pacific North America and 48 per cent for 

 Europe. Ninety genera are given as common to Japan and America, 

 which are absent from Europe, and of these the greater part are also 

 wanting on our Pacific coast. Among the most characteristic of 

 these may be mentioned Magnolia, Nelumbo, Ampelopsis, Wistaria, 

 Hydrangea, Hamamelis, and Catalpa. 



A study of these forms reveals the interesting fact that the trees 

 are, almost without exception, genera which are represented in the 

 Tertiary flora of Europe, as well as that of Japan and America, and 

 it is highly probable that the herbaceous plants, like Dicentra, Podo- 

 phyllum, Jeffersonia, and other peculiar types of the Asiatic and 

 North American flora, are also descended from Tertiary ancestors. 



The survival 'of these plants in such widely separated regions is 

 accounted for by the topography of the country, which allowed them 

 to retreat southward during the glacial period, and to reestablish 

 themselves northward with the increasing warmth. The climatic 

 conditions of the present are very similar in the two regions, and 

 are suited to the needs of these plants. Their absence from those 

 parts of Europe where the climatic conditions are suited to their 

 growth is due to their complete extinction during the severe glacier- 

 ation to which all of northern Europe was subjected. 



The absence of these from the Pacific coast is readily explicable 

 from the character of the climate in the warmer parts, which is quite 

 unsuited to the growth of most of these forms. 



The occurrence of the same or closely related species of the same 

 genus in widely separated regions can also be explained usually as 

 survivals of a once widespread type. A well-known case is the 

 genus Torreya, a Conifer of the Yew-family. Four species are now 

 known, one in Florida, one on the Pacific coast, and two in China 



