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Darwin Correspondence Project

From Asa Gray   [10 July 1860]1

– Your observation on Primroses relates to a subject with the general facts

which I am very familiar, though I never thought of the accurate investigation by measurements &c you undertake. I have long ago convinced myself that the two forms are both fertile, but always looked at it as the first step toward bisexuality. When your notion about the probable necessity of cross-fertilization came to my knowledge, these diœcio-dimorphous flowers (See Torr. & Gray, Fl. N. Amer. 2. p. 38)2 occurred to me as a pretty case of arrangement for it. The case is extremely common, in very various families,— tho‘ I did not know it in Primulaceæ. The Rubiaceæ, Borragineæ, Labiatæ, &c &c. are full of it. I think cases can be found of its gliding into structural unisexuality.

Adieu, dear Darwin, | Truly Yours | A. Gray

CD annotations

End of letter: ‘See Manual of Bot | p. 171’3 blue crayon


Dated by CD’s statement in the letter to Asa Gray, 11 August [1860]: ‘I received your note of July 10th’. See also n. 3, below.
Torrey and Gray 1838–43.
CD did not own a copy of Torrey and Gray 1838–43. The expression ‘diœciously dimorphous’ is discussed in Gray’s Manual of botany (Gray 1856, p. 171 n.). In CD’s annotated copy of this work (Darwin Library–CUL), this expression is underlined in pencil. CD thanked Gray for these ‘valuable hints’ in the letter to Asa Gray, 11 August [1860].


Cases of "dioecio-dimorphism" as in primroses are widespread. AG always considered them the first step toward bisexuality.

Letter details

Letter no.
Asa Gray
Charles Robert Darwin
Sent from
Source of text
DAR 110 (ser. 2): 77
Physical description
ALS 1p inc †

Please cite as

Darwin Correspondence Project, “Letter no. 2819,” accessed on 14 July 2024,

Also published in The Correspondence of Charles Darwin, vol. 8