I cannot and ought not to forget that all your time is employed in work certain to be valuable.

It is superfluous in me to say that I enjoy exceedingly writing to you, and that your answers are of the greatest possible service to me.

I return with many thanks the proof on Aquilegia (43/1.

This seems to refer to the discussion on the genus Aquilegia in Hooker and Thomson's "Flora Indica," 1855, Volume I., Systematic Part, page 44.

The authors' conclusion is that "all the European and many of the Siberian forms generally recognised belong to one very variable species." With regard to cirripedes, Mr.Darwin spoke of "certain just perceptible differences which blend together and constitute varieties and not species" ("Life and Letters," I., page 379).): it has interested me much.