428 CORRESPONDENCE. [1857, 



generic, and how many words will you allow each to 

 consist of ? 



Give me your names through some family, say 

 Ranunculacese. If I can see my way clear, I shall 

 follow your lead, or cause it to be followed on an occa- 

 sion which will soon be presented. 



I wish I had known of Clitoria Mariana-acuminata, 

 etc., in time to add it to my list in the last number of 

 " Silliman's Journal ; " a copy of the article was sent 

 to Dr. Hooker by post last week. I will send more, 

 from my extras, presently. 



I am quite prepared for what you say about inter- 

 change of species of United States and Europe taking 

 place via Asia, instead of across the Atlantic ; but you 

 will see there are a few, besides aquatics (Subularia, 

 Eriocaulon, etc.), which would seem to have taken the 

 shorter cut. 



As respects identical species, interchange is the 

 only thing that, on our views of what a species is, will 

 explain the occurrence of the same species here and 

 there. But as to genera, I do not yet feel free to 

 assume an interchange, or a former continuity of land, 

 between two widely separated regions on account of 

 their having identical genera or closely related species. 

 I see no reason why cognate species may not have 

 been originally given to most widely separated sta- 

 tions ; and, as to the facts of association, can we say 

 more than this, that the species of a genus are apt 

 to be confined to one part of the world ? Are there 

 not too many cases to the contrary to warrant our 

 suspecting former continuity of two remote districts 

 on account of common genera ? Peculiar genera, 

 such as Torreya, Illicium, Philadelphia, Astilbe, etc., 

 divided between Japan and the United States of 



