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Darwin Correspondence Project

From W. E. Darwin   20 June [1866]1


June 20

My Dear Father

I enclose you some orders for dividends for your signature   please forward them to Uncle Ras,2 and ask him to sign & post them.

I cannot help thinking the Rhamnus is a case of dimorphic becoming diœcious;3 I will tell more in a day or two but I have not time today, & George & Edmund come here tomorrow.4 I thought it must be as you say at first, but I found that the pollen of long pistilled male was the largest, which seemed odd if that was less of a male flower than the short pistilled;5 so I examined the female flowers, & I think I have found two sizes among them corresponding to the two males flowers.6 Mem. I am probly. wrong; will write in a day or two

your affection— | W. E. Darwin

CD annotations

1.1 I enclose … post them 1.2] crossed blue pencil
2.3 I found … largest 2.4] underl red pencil


The year is established by the relationship between this letter and the letter to W. E. Darwin, 19 [June 1866].
The reference is to Erasmus Alvey Darwin.
In his letter to William of 19 [June 1866], CD stated that he thought Rhamnus cathartica had once existed in hermaphrodite and female forms, and that he saw no evidence that it had ever been dimorphic.
William refers to his brother George Howard Darwin and their cousin Edmund Langton.
In his research on Primula, CD had observed that pollen-grains from short-styled forms were consistently larger than those from long-styled forms (see ‘Dimorphic condition in Primula’, pp. 78–9; Collected papers 2: 45–7; see also ‘Three forms of Lythrum salicaria’, pp. 178, 190–1; Collected papers 2: 113, 123, 125). In Forms of flowers, p. 294, he noted William’s ‘very remarkable’ observation that larger pollen-grains were produced in male flowers with longer, rather than shorter, pistils, in Rhamnus cathartica. CD added that heterostyled plants tended to produce larger pollen-grains in flowers with shorter pistils, but that R. cathartica showed no evidence of having ever been heterostyled.
William’s notes on Rhamnus cathartica are in DAR 186: 43 and contain sketches of the four flower forms. In Forms of flowers, pp. 294–5, CD described Rhamnus cathartica as dioecious, with each sex having two ‘sub-forms’. See also letter from W. E. Darwin, [18 June 1866] and n. 2, and letter to W. E. Darwin, 19 [June 1866] and n. 4.


Thinks Rhamnus is a case of a dimorphic plant that has become dioecious.

Letter details

Letter no.
William Erasmus Darwin
Charles Robert Darwin
Sent from
Source of text
DAR 109: A77
Physical description
2pp †

Please cite as

Darwin Correspondence Project, “Letter no. 5128,” accessed on 18 October 2017,

Also published in The Correspondence of Charles Darwin, vol. 14