Letter-writing was a space in which women, who were excluded from universities, professional societies, and most specialist journals, could participate in science. Darwin corresponded with a number of women, especially in the field of botany, drawing on their expertise and encouraging their work privately. This collection of letters provides a window into his interaction with scientific women.
Letter 4170 — Becker, Lydia to Darwin, C. R., 18 May 1863
This is a very formal letter written in the third person by Lydia Becker to Darwin. Becker sends flowers of a variety of Lychnis dioica which has bisexual flowers.
Letter 4258 — Becker, Lydia to Darwin, C. R., 31 July 
Becker has found seeds produced by an hermaphroditic Lychnis and will send them. She also discovered some structural obstacles to fertilisation of hermaphrodite Lychnis.
Letter 4260a — Darwin, C. R. to Becker, L. E., 2 Aug 
Darwin thanks Lydia Becker for the Lychnis seed [see 4258], which he will plant in the hope of fertilising the little ovaria. He comments on the two forms of Linum.
Letter 4441 — Becker, Lydia to Darwin, C. R., 30 Mar 1864
Becker sends Darwin a copy of her book [Botany for novices (1864?)], intended to encourage the young, especially ladies, to study nature.
Letter 115 — Darwin, C. R. to Darwin, S. E., [4 Sept 1831]
Darwin writes to his sister Susan. He spent preceding day with Henslow; much had to be done. His friend, Alexander Charles Wood, has written to Capt. FitzRoy about Darwin. Peacock offered the Beagle naturalist appointment first to Leonard Jenyns, who almost accepted, as did Henslow himself. Darwin will talk to Capt. Francis Beaufort [Hydrographer] and FitzRoy. He also sends his thanks to all his family.
Letter 1176 — Darwin, C. R. to Darwin, Emma, [20–1 May 1848]
Darwin writes to his wife Emma. The letter is a combination of personal and scientific matters. He reports on his father’s health, as well as sister Catherine’s and his own. He also notes that Hensleigh [Wedgwood] thinks he has settled the free-will question -– “we have none whatsoever”. He notes that she was right to send the barnacles and gives directions on their care.
Letter 7124 — Darwin, C. R. to Darwin, H. E., [before 17 Feb 1870]
Darwin writes to his daughter Henrietta [Etty]. He sends MS [of chs. 3 and 4, “Comparison of the mental powers of man and the lower animals”, Descent] for her criticism. Darwin fears parts of it are too much like a sermon; “who wd ever have thought I shd turn parson?”
Letter 5585 — Darwin, C. R. to Darwin, H. E., 26 July 
Darwin writes to his daughter Henrietta [Etty]. He prefers not to send her proof-slips of the present chapter [of Variation], which has been enormously altered, but will be glad to have her see slips and revise in the future. He praises her remarks, criticisms, doubts, and corrections.
Letter 5745 — Barber, M. E. to Darwin, C. R., [after Feb 1867]
In this letter, naturalist, artist, and writer Mary Elizabeth Barber replies to Queries on expression based on observations of the Kaffir and Fingoe tribes in South Africa.