Gives some observations on the sensitivity of Drosera species and comments on cases of "dioecio-dimorphism".
to carry down the pollinia, taken from one flower on the point of a fine needle, to the stigma of another flower, have failed,—the pollinia lodging above the stigma or over on the dorsal face. I enclose a spike of S. cernua.
The most marked diœcio-dimorphous flowers I know are in Rubiaceæ, and the most familiar cases are in Houstonia (Oldenlandia, but the old name & genus will be restored) specially our H. purpurea and the everywhere common H. cærulea, and Mitchella repens. Spermacoce virginiana & Diodia teres, also show it. I have no data for a list; but the cases are numerous. I will make any observations you will indicate next spring.
What you say of Mill well accords with what Prof. Henry of Smithsonian
- f1 3242.f1The date is established by CD's statement in the letter to Asa Gray, 17 September , that he had just received Gray's letter `of Aug
t27 th& 29 th& Sept 2 d'.
- f2 3242.f2CD had asked Gray, in his letter of 21 July , to `have a look at Spiranthes' in order to confirm his description of the orchid's flower structure. Gray had apparently found differences in the sexual parts of American species of Spiranthes. See also letter to Asa Gray, 17 September .
- f3 3242.f3CD had suggested that Gray might like to observe the sensitivity of Drosera leaves to substances placed on them (see letter to Asa Gray, 17 February ). The thread-leaved sundew, D. filiformis, is common in wet, sandy, coastal areas from Massachusetts southward. See also letter to Asa Gray, 21 July .
- f4 3242.f4CD had asked Gray whether he knew of any dimorphic plants in which the two flower forms occur on separate plants living commingled in the same area (see letter to Asa Gray, 5 June ). In his Manual of the botany of the northern United States, Gray defined the term `diœciously dimorphous' in the section describing the Rubiaceae, stating that in `several genera, such as Mitchella, Oldenlandia, &c., the flowers, although perfect, are of two sorts in different individuals', one with `exserted' (protruded) stamens and short styles and the other `included' stamens and long styles (A. Gray 1856, p. 171 n.). The term had first been defined in Torrey and Gray 1838--43, 1: 38. See also letter from Asa Gray, 11 October 1861.
- f5 3242.f5See the letter to Asa Gray, 21 July , in which CD mentioned that John Stuart Mill considered CD's reasoning in Origin to be `in the most exact accordance with the strict principles of logic.' The physicist, Joseph Henry, was the secretary and director of the Smithsonian Institution in Washington, DC.