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Darwin Correspondence Project

To W. E. Darwin   14 May [1864]1

Down. | Bromley. | Kent. S.E.

May 14

My dear William

You have really done the work splendidly   I shall say in my paper that you first observed the fact & I shall give all the description on your authority.2 By aid of an old letter you have counted I think you have counted above 200 plants.3 I have looked again & I can see length of anthers is extremely variable.4 Theoretically the anthers of long-styled ought to be shortest & so I have generally found them5   If you have any flowers in bud & can spare time, open them & compare the indehissent anthers of the 2 forms, for this is of some real importance. It seemed to me that the anthers of long styled with smaller pollen-grains contain many more shrivelled & worthless grains: this theoretically ought to be so but I compared only 2 anthers6   the enclosed diagram will explain what I can pretty plainly see will be the result of my crosses.7 The case is quite new & will explain I believe a whole class of cases like that of common thyme.8

yrs. C.D.

(Your slavey’s keep will cost about 22£ a year but that is no reason against her if she will be useful on the whole).

Aunt Eliz. is coming today.9

yours dear W.

P.S. Frank10 told me that some rarish Echium grew on shore near S—ampton. When in flower I shd much like to hear about its flowers, whether dimorphic like Pulmonaria, or like our Echium, with anthers quite aborted in one form.—11

I shd like to see its flowers


Long-styled Pulmonaria Short-styled

The 3 black unbroken lines show perfect fertility

The 1 dotted line shows complete sterility.

The anthers of long-styled are, I believe, tending to abortion.13

The ancestor of Echium vulgare I believe was once in exact state of Pulmonaria, the anthers of long-styled having since quite aborted—14


The year is established by the relationship between this letter and the letter from W. E. Darwin, 12 May [1864].
CD published a discussion of Pulmonaria angustifolia in Forms of flowers, citing William’s observations on pp. 105, 106, and 107 (see letters from W. E. Darwin, 18 April 1864 and n. 3, and 12 May [1864] and nn. 3 and 4).
CD is referring to William’s letter of 12 May [1864] and to his earlier letter of 4 May [1863] (Correspondence vol. 11) in which he mentioned collecting 52 plants (see also DAR 110: A41 and A53). In Forms of flowers, p. 107, CD noted that William had collected 202 plants on the Isle of Wight.
CD recorded this observation in a note dated 14 May in DAR 110: A51 v. See also letter from W. E. Darwin, 12 May [1864] and n. 6, and Forms of flowers, p. 106.
CD had recently determined that in many heterostyled plants, the anthers, like the pollen-grains, were often smaller in the long-styled forms (see letter to W. E. Darwin, 3 May [1864], n. 2, and ‘Three forms of Lythrum salicaria’, pp. 171–4 (Collected papers 2: 108–9). As a result of this, and other structural differences between the two forms that he had observed, he concluded that many heterostyled plants were ‘tending to become diœcious’ (Forms of flowers, p. 257), or in some cases what he later called gyno-dioecious; in either case, the anthers would become rudimentary in the long-styled form (see nn. 8, 11, 13, and 14, below, and Forms of flowers, pp. 107, 287, 298–9). In Forms of flowers, p. 252, CD noted the ‘remarkable difference between the forms of several heterostyled species, namely in the anthers of the short-styled flowers, which contain the larger pollen-grains, being longer than those of the long-styled flowers’. He described several species in addition to Pulmonaria angustifolia in this regard, adding that anther sizes had not been ‘particularly attended to in the two forms of the other heterostyled plants’. He discussed anther length in P. angustifolia in more detail in Forms of flowers, pp. 106 and 252.
CD had earlier determined that the occurrence of smaller pollen-grains in a long-styled plant was often an indication of dimorphism (see, for example, ‘Dimorphic condition in Primula’, p. 79 (Collected papers 2: 46); see also letter from W. E. Darwin, 14 April [1864] and n. 4, n. 5, above, and Forms of flowers, pp. 3, 248–52). William had already sent sketches of Pulmonaria angustifolia pollen from opened flowers, evidently measured wet, with his letters of 14 April [1864] and 18 April 1864. CD compared the unopened (indehiscent) anthers on 6 May 1864 (see letter to W. E. Darwin, 3 May [1864], n. 2). In Forms of flowers, p. 106, CD noted the smaller anther size in the shorter stamens of the long-styled form, adding that ‘a larger proportion of the grains were small, shrivelled, and worthless’. In Forms of flowers, pp. 106 and 249, CD gave comparative measurements of the pollen-grains.
In CD’s diagram, the dotted line indicates that self-pollination in the long-styled flower resulted in sterility (see n. 13, below). CD crossed the different forms of Pulmonaria angustifolia in 1864 and 1865; for CD’s experimental notes on these crosses, see DAR 110: A44–55; for his published results, see Forms of flowers, pp. 107–10.
In 1863, CD had evidently speculated on whether Pulmonaria angustifolia might represent a transition from heterostyly to what he later called ‘gyno-dioecism’, in which species include hermaphrodite and female individuals on different plants; he had already observed gyno-dioecious forms in Thymus and Echium (see Correspondence vol. 11, letters to W. E. Darwin, [5 May 1863] and n. 6, and [10 May 1863] and n. 3). CD discussed gyno-dioecism in thyme in Forms of flowers, pp. 298–303. His notes on thyme are in DAR 109: A21–2, A28, A45–6 v. and in his experimental notebook (DAR 157a: 72). He recorded observations of thyme in the garden at Down on 5 May and 28 May 1864 (DAR 109: A46 v.).
According to Emma Darwin’s diary (DAR 242), Emma’s sister Sarah Elizabeth Wedgwood visited Down from 14 to 17 May 1864.
Francis Darwin.
CD had observed the two forms of Echium vulgare, one with rudimentary anthers, at Down in 1862; his note, dated 6 August 1862, included the statement, ‘Case like Thymus’ (see DAR 109: A13). CD had decided that Echium, like Thymus, was gyno-dioecious (see Correspondence vol. 10, letter to Asa Gray, 9 August [1862] and n. 8, n. 8, above, and Forms of flowers, pp. 111, 305–6). A letter from William answering CD’s query has not been found; however, a note in DAR 109: A14 records that Francis Darwin collected specimens of Echium vulgare for CD in June and July 1864 from Down and another site (see also Forms of flowers, p. 306).
The diagram is reproduced at 75 per cent of its original size.
As he expected, CD’s crossing experiments did reveal sterility only in the self-pollinated, long-styled form (see nn. 7 and 8, above). See also diagrams in DAR 110: A42 and DAR 111: B38.
See nn. 7, 8, and 13, above. CD considered a transition from the dimorphism of Pulmonaria to the gyno-dioecism of Thymus in a note in DAR 109: A34 v. In Forms of flowers, p. 287, CD noted his suspicion that the long-styled form of Pulmonaria angustifolia was ‘tending to become female’ without the other form becoming male; however, see also Forms of flowers, p. 107. CD discussed the possibility of some of the gyno-dioecious Labiateae originating from individuals producing less pollen in Forms of flowers p. 304. For his general remarks on this possible transition, see ibid., pp. 278–9.


Discusses WED’s observations on polymorphic flowers.

Letter details

Letter no.
Charles Robert Darwin
William Erasmus Darwin
Sent from
Source of text
DAR 97: A1–2, A4–5
Physical description
5pp inc sketch

Please cite as

Darwin Correspondence Project, “Letter no. 4495,” accessed on 26 March 2019,

Also published in The Correspondence of Charles Darwin, vol. 12