RECORD: Darwin, C. R. 1874. [Irritability of Pinguicula]. Gardeners' Chronicle and Agricultural Gazette no. 2 (4 July): 15.
REVISION HISTORY: Scanned, OCRed, corrected and edited by John van Wyhe 2003-8, textual corrections by Sue Asscher 3.2007. RN3
Most of us remember the use that PALEY made of the watch as an evidence of design, and of necessity of a designer.1 Twenty or thirty years ago this doctrine suffered by injudicious illustration, and a new school arose deriving its chief inspiration from GOETHE. Modifications in form were set down as variations from an ideal pattern or type, and adaptations to special ends, though admitted in some cases, were discredited in others. Not the least service which Mr. DARWIN has rendered to science has been the demonstration that many adaptations formerly supposed either to be of trifling moment or purposeless illustrations of a particular preordained pattern, are really adaptations to special purposes, or, at least, are the relics of traces of former adaptation of this kind. While some naturalists have been counting spots and measuring scales, splitting hairs 'twixt south and south-west sides, disputing whether there are two or twenty species of Brambles, or referring every little bump to a theoretical typical form, Mr. DARWIN has been quietly and steadily setting to work to show the purpose and meaning of various organs and rudimentary structures. In this manner he has made clear the use and purport of many parts and variations in plants, the study of which was before to a large extent barren in results. In thus affording a rational and intelligible explanation of many structures and phenomena, Mr. DARWIN has not only advanced physiological science to a high degree, and infected others with the desire so far as their means and abilities are concerned to do likewise, but he has placed a most effective weapon in the hands of those who, like PALEY, attach very high importance to the study of Natural Theology. Our pages of late years have teemed with illustrations of adaptations of structure to function, especially with regard to the fertilisation of flowers by insects. Only lately, through the kindness of Dr. ASA GRAY,2 we have had occasion to lay before our readers the curious arrangements by which Droseras and Sarracenias obtain some at least of their nourishment by entrapping and digesting insects. Dr. SANDERSON3 has shown us how the movement of the leaves of Venus' Fly-trap Dionæa is accompanied by electrical phenomena, as in the case of the muscles of animals. One of the most curious illustrations yet made known, showing the relation of structural form to definite purpose in the economy of the plant, is that laid before the Scientific Committee on Wednesday last by Mr. DARWIN. Mr. DARWIN'S researches are not yet fully completed, and at some future time he will give a fuller account of his researches, meanwhile no reader will fail to see the exceeding interest of the phenomena we now proceed to relate:—
"The leaves of Pinguicula vulgaris,4 according to Mr. DARWIN, possess a power of digesting animal matter similar to that shown by the Sundews (Drosera). Albumen, fibrin, meat or cartilage induce a secretion from the glands of the upper surface of the leaf, and their secretion becomes feebly acid (but not so much so as that of Drosera). Their secretion is reabsorbed, and causes an aggregation of the protoplasm in the cells of the glands, such as had been observed in other similar cases. Before excitement the glands were seen to be filled with a homogeneous pale greenish fluid; after the aggregation of the protoplasm it can be seen to move. When a row of insects or of Cabbage seeds are placed near the margin of a leaf (or when a single insect is placed at one point,) the whole margin (or one point) becomes curled considerably over in two or three hours; the apex of the leaf will not turn over towards the base. Small fragments of glass also cause a similar movement, but to a much less degree. The inflexed margin pours forth a secretion which envelopes the flies or seeds, but pieces of glass cause no, or hardly any, increase of secretion. But here comes a puzzle: If the flies or fly be removed, the margin of the leaf turns back in less than twenty-four hours; but it does so also when a row of flies and Cabbage seeds are left adhering; so that the use or meaning of the inflexion is at present quite a puzzle."
We must await the publication in full of Mr. DARWIN'S researches before we can say more on the subject. Meantime, as many of our readers will speedily be hieing northwards to the moorlands, where Pinguicula grows, and where Drosera is abundant, we would fain hope that some of them will be enabled to watch the plants in question, and ascertain what insects are entrapped, and under what circumstances.
1 Paley 1809, p. 1.
2 Gray 1874.
3 John Scott Burdon Sanderson (1828-1905), pathologist and physiologist. Sanderson 1873a and 1873b.
4 Pinguicula = butterworts. Darwin's report was read to the Royal Horticultural Society on 1 July and was also reprinted in Nature (30 July) p. 258. Darwin's results were published in Insectivorous plants, chapter 16.
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Citation: John van Wyhe, editor. 2002-. The Complete Work of Charles Darwin Online. (http://darwin-online.org.uk/)
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