I was aware of Darwin's views fourteen years before I adopted them and I have done so solely and entirely from an independent study of the plants themselves.[Letter to W.H. Harvey]

I expect to think that I would rather be author of your book [The Origin of Species] than of any other on Nat. Hist. Science.[Letter to Charles Darwin 12 Dec 1859]

In [David] Douglas's success in life ... his great activity, undaunted courage, singular abstemiousness, and energetic zeal, at once pointed him out as an individual eminently calculated to do himself credit as a scientific traveler.

I am above the forest region, amongst grand rocks & such a torrent as you see in Salvator Rosa's paintings vegetation all a scrub of rhodos. with Pines below me as thick & bad to get through as our Fuegian Fagi on the hill tops, & except the towering peaks of P. S. [perpetual snow] that, here shoot up on all hands there is little difference in the mt scenery—here however the blaze of Rhod. flowers and various colored jungle proclaims a differently constituted region in a naturalist's eye & twenty species here, to one there, always are asking me the vexed question, where do we come from?[Letter to Charles Darwin 24 Jun 1849]