452 A CENTURY OF SCIENCE 



Dr. Gray soon put the Darwinian hypothesis to a 

 severe test. In the Journal for 1840 he had called atten- 

 tion to the remarkable similarity which exists between 

 the flora of Japan and a part of the temperate portion of 

 North America. The first notice of this subject by him 

 occurs in a short review of Dr. Zuccarini's " Flora 

 Japonica," a work based on material furnished by 

 Dr. Siebold, who had long lived in Japan. In this 

 review (39, 175, 1840), he enumerates certain plants com- 

 mon to the two regions, and says, "It is interesting to 

 remark how many of our characteristic genera are repro- 

 duced in Japan, not to speak of striking analogous 

 forms." In a subsequent paper (28, 187, 1859), he recurs 

 to this subject, and, after alluding to geological data fur- 

 nished by J. D. Dana, he says : 



* ' I cannot resist the conclusion that the extant vegetable king- 

 dom has a long and eventful history, and that the explanation 

 of apparent anomalies in the geographical distribution of species 

 may be found in the various and prolonged climatic or other 

 vicissitudes to which they have been subject in earlier times; 

 that the occurrence of certain species, formerly supposed to be 

 peculiar to North America, in a remote or antipodal region, 

 affords in itself no presumption that they were originated there, 

 and that interchange of plants between eastern North America 

 and eastern Asia is explicable upon the most natural and gener- 

 ally received hypothesis (or at least offers no greater difficulty 

 than does the arctic flora, the general homogeneousness of which 

 round the world has always been thought compatible with local 

 origin of the species) and is perhaps not more extensive than 

 might be expected under the circumstances. That the inter- 

 change has mainly taken place in high northern latitudes, and 

 that the isothermal lines have in earlier times turned northward 

 on our eastern and southward on our northwest coast, as they 

 do now, are points which go far towards explaining why eastern 

 North America, rather than Oregon and California, has been 

 mainly concerned in this interchange, and why the temperate 

 interchange, even with Europe, has principally taken place 

 through Asia." 



This paper was communicated in 1859, on the eve of 

 the publication of Darwin's "Origin of Species.'- At a 

 later date he applied the Darwinian theory to the possi- 

 ble solution of the problem, and came to the conclusion 

 that the two floras had a common origin in the Arctic 



