From Asa Gray to Francis Darwin 17 December 1880
Dec. 17. 1880
Dear Mr. Francis Darwin
I should have explicitly said, last evening, if I had my wits at command, that I had heard enough of your paper to be assured that you had elaborately proved that Sachs has greatly overworked the principle of gravity. I had always supposed so, at a Venture. But there is nothing so good as proof.
What I wish to suggest is, whether, in the case of your proliferous brambles there is any need to suppose a reversal of ordinary tendencies and actions. Any part of stem may give rise to roots under favoring conditions; but they spring in preference, I think, from nodes, and of course from young parts, In a cutting a callus first forms to heal the cut surface; and from this, as being fresh tissue roots are produced. That a cutting should form this callus (and therefore produce roots) more readily from the lower than from the apical end may well be correlated with the general tendency or action in the bark (which is chiefly here concerned) through which the pabulum for growth is distributed downward.
The tip of the bramble-shoot touching the ground may root more readily than a basal part of the stem would, only because it is younger. Perhaps it is not the very apex that forms roots, but a piece consisting of several very short inter-nodes and their nodes (and which thickens and becomes slightly tuber-like if I rightly understand); and the roots may really spring from these nodes, i.e. from the base of each inter node. That may be putting a fine theoretical point upon it. But altogether is there any need to suppose that such bramble shoots act reversely to ordinary stems? That is, as to rooting. Could you not directly test this, by cutting up a long pendent bramble-shoot in to cuttings, making the sections through the middle of internodes of considerable length, each cutting to consist say of one whole internode and an upper and a lower half internode,— or to be longer, if that would render them easier to strike,— and then insert half of them with the organically upper, half with the lower end into the sand for rooting. If, contrary to what is normal, they rooted best from the upper end, there would indeed be a reversal of the ordinary tendency; and very singular that would be.
Pray excuse my writing on a matter that I practically know nothing about, and believe me to be
Very truly Yours, | Asa Gray
Roots arising from stems and shoots of brambles.
Please cite as
Darwin Correspondence Project, “Letter no. 12921,” accessed on 4 December 2016, http://www.darwinproject.ac.uk/DCP-LETT-12921