CHAPTEK XXXVIII 



AMERICA : AND GEOGRAPHICAL DISTRIBUTION 



Che outstanding event of 1877 was the long looked for visit 

 o the United States. This had been half-planned for the 

 ast four years. America had a two-fold call for Hooker, in 

 he problem of the North American Flora and the friendship 

 vith Asa Gray. These represented the personal and impersonal 

 :ides of the same impulse. Their common interest in the same 

 mestion, approached from different sides, had initiated an 

 inbroken correspondence which deepened in personal and 

 cientific interest with their united appreciation of Darwin. 

 }ray had already visited England four times, and was urgent 

 or Hooker to come over and join him in a personal study of 

 he complexities of botanical distribution in the States. 



Two features in the problem which cried most loudly for 

 explanation were the remarkable connexion between the 

 )lants of the Eastern States and those of Eastern Asia and 

 Tapan — with no living intermediate connexions — and the 

 Lard line of division between the Arctic floras of America 

 .nd Greenland. Independently of each other, Gray had in- 

 stigated the former x and Hooker the latter. 2 Both came 

 >ack to a common cause in the Glacial Period and the earlier 

 and connexion with an Arctic continent. 



But why had not the Glacial Period produced the same 



1 ' Observations upon the Relations of the .Japanese Flora to that of 

 <orth America, and of other parts of the North Temperate Zone,' Memoirs of 

 he North American Academy of Sciences, vol. vi. p. 377. Read December 14, 

 858, and January 11, 1859. 



1 ' Outlines of the Distribution of Arctic Plants.' Read before the Linn. 

 ioc, June 21, 1860. Trans. Linn. Soc, xxiii. p. 257. 



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