From Asa Gray [1 April 1880]
Sir, Ipomœa leptophylla makes a root as big as a man. So does Ipomœa pandurata,—which, I believe—but dont know—germinates normally, That must be looked to. If it has the same trick it would well confirm your notion of the meaning of the thing.
Germination and root of Ipomoea.
Please cite as
Darwin Correspondence Project, “Letter no. 12556,” accessed on 13 February 2016, http://www.darwinproject.ac.uk/DCP-LETT-12556