428 CORRESPONDENCE. [1857, 



generic, and how many words will you allow each to 

 consist of ? 



Give me your names through some family, say 

 Ranunculaceae. 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, Philadelphus, Astilbe, etc., 

 divided between Japan and the United States of 



