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." 



t Hooker, J. D., "North American Flora," p. 573. 



