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