TY, 
ET. 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 fh North American 
flora ; in which the dying out of some forms, and their 
roplagastl 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 
atu 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! 
