The year is established by the relationship between this letter and the letter to Asa Gray, 20 March [1880].

See letter to Asa Gray, 20 March [1880]. CD’s own seeds of Ipomoea leptophylla (bush morning-glory) had not germinated (letter to Asa Gray, 19 January 1880). Like Ipomoea pandurata (man-of-the-earth or wild potato vine), it is native to North America; both species, which are perennial, have large tuberous roots. Gray’s comment about the manner of germination refers to earlier correspondence about Megarrhiza californica (a synonym of Marah fabacea, California manroot). CD had described his observations of the germination of plants of this species, noting that soon after germination the growth of the radicle was arrested and the tubular petioles penetrated the ground to a depth of 2 $\frac{1}{2}$ inches beneath the surface (letter to Asa Gray, 19 January 1880).

CD had hypothesised that the tubular petioles of Megarrhiza acted functionally like a root in order to hide the (true) enlarged root from predators during the early stage of its development (letter to Asa Gray, 19 January 1880).