AFFINITIES OF EASTERN PLANTS 
139 
speculations were based on somewhat unreliable foundation. 
We may therefore call to our aid another branch of the geo¬ 
graphical distribution of living organisms, namely that of 
plants, so as to test the validity of these theories. 
Professor Asa Gray * was the first to direct attention, in 
1859, to the striking similarity of the flora of eastern Asia 
to that of the eastern States of North America. In a popular 
account of the distribution of the North American flora, Sir 
Joseph Hooker again alluded to this feature more recently, 
stating that there is actually specific identity in about two 
hundred and thirty cases, and very close representation in 
upward of three hundred and fifty. What is most curious, he 
says, is that there are not a few very singular genera of which 
only two species are known, one in east Asia, the other in 
east America. In some of these instances the Asiatic species 
is a widespread plant in east Asia, whilst the American is an 
extremely scarce and local plant. This and other conditions 
render it conceivable, according to Sir Joseph Hooker,f that 
the Asiatic element in east America is dying out. 
Still more recently Professor Engler discussed the same 
subject very fully. He believes that the number of species 
common to the eastern States and eastern Asia is far less 
than Sir Joseph Hooker thought. Some of these occur also 
in the north, others in western North America. Yet there 
are certain plants which exhibit extraordinarily discontinu¬ 
ous distribution, quite comparable to what we have noticed 
among reptiles. Monotropa uniflora and Phryma lepto- 
stachya, for instance, occur only in the eastern States, in 
Japan and the Himalayan Mountains. Professor Engler 
looks upon these as relicts of a flora which was uniformly dis¬ 
tributed in Tertiary times between the Himalayan Mountains 
and North America. Of the genera Liquidambar, Ostrya, 
Platanus, and Castanea, we know that they lived further north 
in Tertiary times than they do now. We have also learned 
from the Pliocene and Miocene beds of the Rocky Mountains, 
as Professor Engler points out, that the flora west of these 
mountains was formerly not so distinct from that of the 
* Gray, A., “ Relations of Japanese Flora.” 
+ Hooker, J. D., “ North. American Flora,” p. 573. 
