# To Fritz Müller   19 December 1881

Down, | Beckenham, Kent. | (Railway Station | Orpington. S.E.R.) [4 Bryanston Street, London.]

Dec. 19th 1881

My dear Sir

I hope that you may find time to go on with your experiments on such plants, as Lagerstrœmia, mentioned in your letter of Oct. 29th.; for I believe you will arrive at new & curious results, more especially if you can raise two sets of seedlings from the two kinds of pollen.1

Many thanks for the facts about the effects of rain & mud in relation to the waxy secretion.2 I have observed many instances of the lower side being protected better than the upper side, in the case, as I believe, of bushes & trees; so that the advantage in low-growing plants is probably only an incidental one. As I am writing away from my home, I have been unwilling to try more than one leaf of the Passiflora & this came out of the water quite dry on the lower surface & quite wet on the upper.—3 I have not yet begun to put my notes together on this subject, & do not at all know whether I shall be able to make much of it. The oddest little fact which I have observed is that with Trifolium resupinatum one half of the leaf (I think the right-hand side when the leaf is viewed from the apex) is protected by waxy secretion & not the other half; so that when the leaf is dipped into water, exactly $\frac{1}{2}$ the leaf comes out dry & $\frac{1}{2}$ wet.

What the meaning of this can be, I cannot even conjecture.4

I read last night your very interesting article in Kosmos on the leaves of Crotalaria & so was very glad to see the dried leaves sent by you: it seems to me a very curious case.5 I rather doubt whether it will apply to Lupinus, for unless my memory deceives me all the leaves of the same plant sometimes behaved in the same manner.6

But I will try & get some of the same seeds of the Lupinus & sow them in the Spring. Old age, however, is telling on me, & it troubles me to have more than one subject at a time on hand.— Kosmos seems to me a very interesting Journal, & I see there is an article on sexual selection which I must read, as it seems to upset all my conclusions.—7

With all good wishes for you & all your family | believe me, My dear Sir | Yours ever very sincerely | Charles Darwin

## Footnotes

See letter from Fritz Müller, 29 October 1881 and n. 3. Lagerstroemia is the genus of crape myrtle. Müller had noted that up to that point, no seeds derived from fertilisation with yellow pollen had germinated.
Müller had enclosed some leaf specimens with his letter of 29 October 1881, among which were leaves of an unnamed species of Passiflora (passionflower), in which the abaxial surface was protected by a waxy coating (based on Müller’s description, probably P. edulis).
CD had noted the partial absence of bloom (waxy coating) on leaves of Trifolium resupinatum (Persian clover) in the letter to W. T. Thiselton-Dyer, [20–4 August 1877] (Correspondence vol. 25). CD’s observations on the partial absence of bloom, made between 17 August and 21 September 1877, are in DAR 209.12: 178; further notes, dated between 6 July 1881 and 12 April 1882, are in DAR 209.12: 180–2.
Müller’s article on Crotalaria cajanaefolia (a misspelling of C. cajanifolia, chipilin) appeared in Kosmos, December 1881 (F. Müller 1881c).
Lupinus is the genus of lupine. Both Lupinus and Crotalaria (the genus of rattlebox) are in the family Fabaceae. Müller had observed that young leaflets of C. cajanaefolia behaved differently from older ones (see letter from Fritz Müller, 6, 7, and 9 September 1881). In Movement in plants, pp. 341–3, CD had discussed the variability of nyctitropic movements in some species of Lupinus and noted that younger leaflets often moved up rather than down at night.
CD refers to an article by Wilhelm von Reichenau, ‘Ueber den Ursprung der secundären männlichen Geschlechts-charaktere, insbesondere bei den Blatthornkäfern’ (On the origin of secondary male sexual characteristics, particularly in lamellicorn beetles; Reichenau 1881). Reichenau argued that many of the characteristics that CD had linked to sexual selection could be better accounted for by natural selection.

## Bibliography

Correspondence: The correspondence of Charles Darwin. Edited by Frederick Burkhardt et al. 29 vols to date. Cambridge: Cambridge University Press. 1985–.

Movement in plants: The power of movement in plants. By Charles Darwin. Assisted by Francis Darwin. London: John Murray. 1880.

Müller, Fritz. 1881f. Eine Pflanze, welche bei Nacht die Himmelsgegenden anzeigt. Kosmos 10: 212–14.

Reichenau, Wilhelm von. 1881. Ueber den Ursprung der secundären männlichen Geschlechts-charaktere, insbesondere bei den Blatthornkäfern. Kosmos 10: 172–94.

## Summary

Waxy secretion or "bloom" on leaves.

FM’s article on Crotalaria.

## Letter details

Letter no.
DCP-LETT-13564
From
Charles Robert Darwin
To
Johann Friedrich Theodor (Fritz) Müller
Sent from
London, Bryanston St, 4 Down letterhead
Source of text
The British Library (Loan MS 10 no 57)
Physical description
ALS 4pp