218 AMERICA : GEOGRAPHICAL DISTRIBUTION 



as a barrier, regarding the dry extreme climate of the South 

 shore as sufficient to kill any Northern Pliocene that might 

 have arrived there. Also who knows what may turn up in 

 the Pliocene of N. Africa ? 



I have been comparing E. States Flora with Calif ornian, 

 and am more than ever amazed at the difference even in 

 such an order as Caryophylkae. 



I hope that you will indicate to me any views or papers 

 of yours that you think I may have overlooked or am likely 

 to overlook. I intend to show, first how your researches 

 on the Japan Flora and mine on the Arctic each come in, 

 and are foundations upon which we meet in theory (one 

 of us in England, the other in America), and how we coalesce 

 as to results in our present labors after travelling together. 

 How ever I shall get the Lecture finished, i.e. the subject 

 properly elaborated, I do not see, for I am really busier 

 than ever ! 



Talking of the E. and W. Floras of N. America, I am 

 surprised to find so many Asiatic types in W. America that 

 are not in East ; and the Western American representatives 

 of Asia seem to belong to a different type from the Eastern 

 American representatives. Can both (the East and the 

 West Asiatic types) have branched off from one Asiatic 

 migration into N. America ? or were there two migrations 

 at very different periods, one into East, the other into West ? 

 if so which first ? I have not read up this matter ; please 

 tell me where to look. 



The full botanical results were worked over when Asa Gray, 

 on his visit to Europe in 1881-2, spent a couple of months at 

 Kew, thereafter joining the Hookers on a spring trip to the 

 Continent. The work was issued conjointly in the Bulletin 

 of the U.S. Geological Survey for 1882, vol. vi, pp. 1-62, under 

 the title of ' The Vegetation of the Rocky Mountain Region 

 and a Comparison with that of other Parts of the World,' by 

 J. D. Hooker and Asa Gray, albeit Hooker, enquiring after 

 progress on August 2, 1879, had written : ' Dare I ask what 

 has become of our report ? I will do anything you like but 

 have my name put before yours.' 



The following letters deal with the progress of the work. 



