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Darwin Correspondence Project

From W. T. Thiselton-Dyer   [June 1877 or later]1

Royal Gardens Kew

Trans: Med. & Phys. Soc.

Calc. vij pp. 221–2242

I avail myself of this opportunity for making a few remarks relative to the production of glaucedo or bloom of plants. Although this substance in a remarkable degree covers all the pubaceous parts of our plant Hitchenia glauca,3 wall. (which in fact derives its specific name from the circumstance), and is in fact easily separable, yet it cannot be altogether removed, as is proved by the surface beneath always continuing opaque and of a dull-green pallid colour; nor is a fresh or exterior layer again reproduced when once it has been rubbed off. In the common castor oil plant, the case is quite different. Here the bloom is likewise very copious and easily separable, but after being removed, the surface below appears quite shining, and it is reproduced again as often as it is removed. Several plants of the red variety, which had been raised from seeds sent down from the Botanic Garden of Saharunpore, in 1832, were growing within a few feet from each other in one of the nurseries of the Calcutta Garden; they measured from 12 to 14 feet in height. One of these plants was densely covered throughout with glaucedo; all the other individuals were perfectly destitute of it, and had a uniformly red and glossy surface. During the rainy season of the succeeding year, in the months of June, July, and August, the following experiments were made. I rubbed off every particle of bloom from the individual first mentioned, so that the stem, branches, and leaves became quite naked and shining. Within a fortnight a thin layer of bloom had already formed, and in six or eight days more, the surface was as much covered as it had ever been before; this process was several times repeated, and uniformly with the same result.4

In Musa glauca, Roxb. the sheaths of the leaves are very thickly covered by a white powdery bloom, which is constantly reproduced.5

The preceding experiments seem to invalidate an observation of De Candolle Phys: viz. ii. 2326

Malgré l’extrême analogie qu’on observe entre la cire excrétée par les feuilles et par les fruits, elle m’a présenté une différence physiologique que je dois mentionner. La poussiére des prunes peut être enlevée plusieurs fois en les brossant doucement avant leur maturité, et à chaque fois elle se reproduit. Celle des feuilles de ficoïdes ou de cacalies une fois enlevée ne s’est pas reproduite, et semblerait être excrétée par les feuilles seulement pendant leur jeunesse.

With respect to the Mesembryanthemum and Cacalia the fact is undoubtedly as stated by the Author7

CD annotations

Top of letter: ‘Wallich’ blue crayon


The date is established by CD’s renewed investigations on bloom (see letter to Fritz Müller, 14 May 1877 and n. 2, and letter to J. D. Hooker, 31 May 1877).
The whole text of this letter is quoted (with a few omissions) from a paper by Nathaniel Wallich published in Transactions of the Medical and Physical Society of Calcutta (Wallich 1834).
Hitchenia glauca is a species of ginger native to Myanmar.
Wallich 1834, pp. 221–2. Saharunpore (now Saharanpur) is in north-west India.
See Wallich 1834, p. 223. Musa glauca is a synonym of Ensete glaucum, the snow banana.
Wallich 1834, p. 223. Wallich quoted from Augustin Pyramus de Candolle’s Physiologie végétale ou exposition des forces et des fonctions (A. P. Candolle 1832, 1: 232; ‘ii’ refers to ‘livre II’, a subdivision of vol. 1). The passage may be translated: In spite of the extreme similarity observed in the wax excreted by leaves and fruits, there is a physiological difference that I must mention. The coating on plums can be removed several times before maturity by brushing gently, and each time it is reproduced. That of leaves of the ficoïde or cacalia once removed does not come back, and would seem to be excreted by leaves only when they are young. Ficoïde is the French common name for ice plants (family Aizoaceae, but Ficoidaceae was a synonym).
Wallich 1834, p. 224. Most species in the genus Cacalia have been subsumed within other genera, such as Adenostyles and Arnoglossum. Mesembryanthemum is a genus of flowering plants indigenous to southern Africa.


Candolle, Augustin Pyramus de. 1832. Physiologie végétale, ou exposition des forces et des fonctions vitales des végétaux. 3 vols. Paris: Béchet Jeune.

Wallich, Nathaniel. 1834. Descriptions of some rare and curious plants. [Read 5 April 1834.] Transactions of the Medical and Physical Society of Calcutta 7: 215–34.


Notes and extracts relating to "bloom".

Letter details

Letter no.
William Turner Thiselton-Dyer
Charles Robert Darwin
Sent from
Source of text
DAR 68: 32–5
Physical description
Amem 7pp †

Please cite as

Darwin Correspondence Project, “Letter no. 10751,” accessed on 21 October 2021,