# To Francis Darwin   26 June [1878]1

Down, | Beckenham, Kent. | Railway Station | Orpington. S.E.R.

June 26th

My dear F.

I have been greatly interested by the scientific part of your letter & we have all been amused by the non-scientific.2 If you have spare time (but not otherwise) I shd like to know from your own researches whether in oat seedlings (say $\frac{1}{10}$ or $\frac{2}{10}$ inch high) whether there is chlorophyll,— So as to make sure that the bending is to find a passage to light for future use.—3

I quite overlooked in Sachs about radicles in Cieslokis’ experiments being dry.—

Keep extract about his statement of sliced radicles turning from the cut side.—4 Please let me hear generic name of plant— hygrometrica: perhaps I cd. borrow spec. from Kew.5

I wonder what made Sachs think about bloom protection against insects: I suppose you mentioned our results with cabbages & Sea-Kale.—6

If you can make it out read the enclosed memorandum & tell me what you think about it.— I fear from reading McNab Pfeffer’s book must be studied.—7 It seems to me that the cotyledons of Oxalis offer a most promising field for study, as in some species, they move vertically up,—in others vertically down—in others only a little movement at night.8

Your affect. old Father | C. Darwin

## [Enclosure]

June 25th 1878. The short petioles of the Cots. of Cassia are enlarged, transversely wrinkled & formed of tissue appearing different from that of lamina & Hypocotyl.— How is Oxalis valdiviana & rosea or floribunda??

I neglected to observe with Cassia whether when Cots. Horizontal upper surface of petiole is transversely wrinkled.—

I have looked at Cots. of Oxalis floribunda & there seems to be a semicircular pale-coloured pulvinus on upper surface formed of smaller cells; but it tired me too much to look carefully.— Now on O. corniculata the cots of which raise only 45° I can see no pulvinus.— This very important showing that pulvinus developed in same genus.9

## Footnotes

The year is established by the date of the enclosure.
Most of the scientific issues dealt with in this letter relate to the letter from Francis Darwin, [22 June 1878]. Presumably another letter containing both scientific and non-scientific material was sent but has now been lost.
In his letter of 18 June [1878], CD had asked Francis to borrow Theophil Ciesielski’s article (Ciesielski 1871) from Julius Sachs and read about the circumstances in which radicles grew upwards away from moisture. The passage about sliced radicles is on p. 33. See also letter from Francis Darwin, [22 June 1878].
See letter from Francis Darwin, [22 June 1878] and n. 6. The Outwards book, p. 463 (Archives, Royal Botanic Gardens, Kew), records that ‘Porliera hygrometrica’ (Porlieria hygrometra) was sent to Down on 5 July 1878.
CD was probably reading William Ramsay McNab’s chapter, ‘Movements of variation in plants’, in McNab’s Botany: outlines of morphology and physiology (McNab 1878, pp. 140–3); the chapter contains a reference to Wilhelm Pfeffer’s Die periodischen Bewegungen der Blattorgane (The periodic movements of leaf organs; Pfeffer 1875).
For CD’s earlier interest in the sensitivity of species of Cassia, see letter to J. D. Hooker, 25 March [1878]. Oxalis valdiviana is a synonym of O. valdiviensis (Chilean yellow-sorrel); O. rosea is pink sorrel; O. floribunda is abundant flowering wood sorrel; O. corniculata is creeping wood sorrel.

## Bibliography

Ciesielski, Theophil. 1871. Untersuchungen über die Abwärtskrümmung der Wurzel. Inaugural-Dissertation welche mit Genehmigung philosophischen Facultät der königl. Universität zu Breslau zur Erlangung der Doctorwürde. Breslau: R. Nischkowsky.

Pfeffer, Wilhelm. 1875. Die periodische Bewegungen der Blattorgane. Leipzig: Verlag von Wilhelm Engelmann.

## Summary

Asks questions related to movement in plants. The cotyledons of Oxalis offer a promising field for study.

Wonders why Julius von Sachs thinks bloom is a protection against insects.

Encloses notes on the cotyledons of Oxalis species.

## Letter details

Letter no.
DCP-LETT-11570
From
Charles Robert Darwin
To
Francis Darwin
Sent from
Down
Source of text
DAR 211: 29–30
Physical description
4pp, encl Amem 1p