The Problems of Plant Distribution 257 



between. Only a few cases can be given here, but 

 these will be sufficient to illustrate the point. The 

 very characteristic tulip-tree (Liriodendron) of At- 

 lantic North America has an almost identically sim- 

 ilar species occurring in China ; the genus Magnolia 

 belongs solely to Eastern Asia and Eastern Amer- 

 ica; Wistaria, Stuartia, Ampelopsis, Hamamelis, 

 and many others show a like distribution. Many of 

 these occur fossil, showing that they were once 

 widespread, and that their present occurrence is a 

 case of survival in widely separated regions where 

 conditions happened to be favorable. While we 

 know from the fossil records that these isolated 

 types of trees and shrubs were once widespread, 

 we can only conjecture that the same was true of 

 certain plants whose distribution is now similar, but 

 of which we have no fossil record. Among the 

 most peculiar plants of Atlantic North America 

 are certain herbaceous plants of the Barberry fam- 

 ily. The mandrake (Podophyllum), and the twin- 

 leaf (Jeffersonia), are examples of these isolated 

 types. Each of these is represented in Eastern 

 America by a single species, and the occurrence of 

 another closely allied species in such remote regions 

 as Japan and the Himalayas, makes it almost certain 

 that these must be Tertiary genera once widespread, 

 which have survived, just as the tulip-trees and 

 magnolias have done in specially favored places. A 

 long list of others might be cited, but one more must 

 suffice. The beautiful trailing arbutus, or May- 



