JET. 54.] TO A. DE CANDOLLE. 529 



being able to assign a vera causa. Heer has the dis- 

 advantage of having no known cause to assign ; but 

 he shows that things do not appear to have proceeded 

 as Darwin's theory requires. It does seem as if there 

 were times of peculiar change as well as of great 

 stability. But were this time of change and that of 

 stability simultaneous for the species of a flora ? And 

 does Heer allow enough for the species which now 

 occur under many forms, — show great polymorphism. 

 I continually meet with these in the North American 

 flora ; in which the dying out of some forms, and their 

 replacing by others, which may well take place in 

 time, would, in effect, just give a change like that to 

 be accounted for. But I cannot say that these varie- 

 ties come in insensibly, very likely not. 



Now, to speak of myself. My summer was much 

 frittered away ; the superintending of the new build- 

 ing for my herbarium just preventing any serious 

 study. The autumn was devoted to the removal and 

 rearrangement of plants and books, and to assisting 

 Charles Wright in the collation and distribution into 

 sets of his collections in Cuba for the last three years 

 past ; very full and interesting collections, and requir- 

 ing much care and labor, on account of this distribu- 

 tion being a continuation of former distributions. I 

 laid out into the sets every specimen with my own 

 hands, Mr. Wright adding the tickets and numbers. 

 It was an immense labor, and was finished only at the 

 close of the last day of the year. . . . 



I mean to prepare for " Silliman's Journal " a brief 

 and simple notice of the edifice for my herbarium, so 

 I will not speak further of it here ; further than to 

 say that I am well satisfied, only I sadly need a cura- 

 tor! 



