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Herbarium of Harvard University, Cambridge, Mass., Feb. 5, 1878. My dear Mr. Muir: I meant to have acknowledged your
kind letter of 13th ult.--took it with me to Washington to write there, but found no time. Had long talk with Miss Sallie
Kennedy, about the glorious time after we separated. What a pity we did not go on with you I am going to send your letter
to-day to Sir Joseph Hooker. When we talk about which is species and which variety, we don't venture to suppose we can tell
which came from the other, or first divided from some common stock. The species is much older than your hot lava, and came
from -- Lord knows where, originally. All we can say is that the supposed form is better adapted to one extreme than to the
other. All your notes are most interesting. Old flexilis is P. albicaulis, that is clear enough. You should have found Pinus
aristata, which, without awn, is P. Balfourinana. Address of Sir J. D. Hooker, Royal Gardens, Kew near London. Ever yours,
Asa Gray