Online Encyclopedia

Search over 40,000 articles from the original, classic Encyclopedia Britannica, 11th Edition.

SUNDEW

Online Encyclopedia
Originally appearing in Volume V26, Page 102 of the 1911 Encyclopedia Britannica.
» Make a correction to this article.
» Add information or comments to this article.
Spread the word: del.icio.us del.icio.us it!

SUNDEW , in See also:

botany, the popular name for a genus of See also:plants known as Drosera (Gr. Sp000r, See also:dew; Fr. rossolis, Ger. Sonnenthau) so called from the drops of viscid transparent glittering secretion See also:borne by the tentacles which See also:cover the See also:leaf-See also:surface. It is a See also:cosmopolitan genus of slender glandular herbs, with leaves arranged in a basal rosette or alternately on an elongated See also:stem, and is represented in See also:Britain by three See also:species, which are found in spongy bogs and heaths. The See also:common sundew (D. rotundifolia) has extremely small roots, and bears five or six See also:radical leaves horizontally extended in a rosette around the See also:flower-stalk. The upper surface of each leaf is covered with gland-bearing filaments or " tentacles," of which there are on an See also:average about two See also:hundred. Each gland is surrounded by a large dew-like drop of the viscid secretion. A small fibro-vascular bundle (b, fig. 3, B), consisting mainly of See also:spiral (After See also:Darwin.) vessels, runs up through the stalk of the tentacle and is surrounded by a layer of elongated parenchyma cells outside of which is the epidermis filled with a homogeneous fluid tinted See also:purple by a derivative of See also:chlorophyll (eryhrophyll). The epidermis bears small multicellular prominences. The glandular See also:head of the tentacle contains a central See also:mass of spirally thickened cells (tracheids) in immediate contact with the upper end of the fibrovascular bundle. Around these is a layer of large colourless thin walled cells which reaches the surface at the See also:base of the head and acts as absorbing cells.

Outside these are two layers (the See also:

outer one the epidermis) filled with purple fluid. See also:Insects are attracted by the leaves; a See also:fly alighting on the disk, or even only touching one or two of the exterior tentacles, is immediately entangled by the viscid secretion; the tentacles to which it is adhering begin to See also:bend, and thus pass on their See also:prey to the tentacles next succeeding them inwards, and the See also:insect is thus carried by a curious See also:rolling See also:movement to the centre of the leaf. The tentacles on all sides become similarly inflected ; the blade or the leaf may even become almost See also:cup-shaped ; and the insect, bathed in the abundant secretion which soon closes up its tracheae, is drowned in about a See also:quarter of an See also:hour. The leaves clasp also, but for a much shorter See also:time, over inorganic bodies. The bending of the tentacle takes See also:place near its base, and may be excited (I) by repeated touches, although not by gusts of See also:wind or drops of See also:rain, thus saving the plant from much useless movement; (2) by contact with any solid, even though insoluble and of far greater minuteness than could be appreciated by our sense of .See also:touch—a morsel of human See also:hair weighing only vaha of a See also:grain, and this (After Dodel-See also:Port.) A, See also:External aspect with drop of secretion; B, See also:Internal stricture. largely supported too by the viscid secretion, sufficing to induce movement; (3) by the absorption of a trace. of certain fluids, mostly nitrogenous. During the See also:inflexion of the tentacle, and even before it touches the stimulating See also:object, the secretion of the gland increases in quantity, and, instead of remaining neutral, becomes See also:acid. The secretion contains a See also:digestive See also:enzyme which renders soluble the nitrogenous substances of the insect's See also:body; these are then absorbed through thin-walled cells at the base of the gland. After absorption the tentacles recurve and the leaf assumes its normal See also:appearance. Closely allied to Drosera is Drosophyllum lusitanicum, which catches such vast See also:numbers of flies in a See also:state of nature that the Portuguese cottagers See also:call it the fly-catcher, and hang up branches of it in their houses for this purpose. Its See also:long narrow leaves are thickly covered with stalked glands, which resemble in the See also:main the tentacles of Drosera, See also:save in that they are incapable of movement, and that the secretion is less viscid and freely leaves the gland to wet the insect, which, creeping FIG. 4.—See also:Part of onward, soon clogs its wings and See also:dies.

There Leaf of Drosophyllum are, moreover, many See also:

minute colourless sessile lusitanicum. glands, which, when stimulated by the absorption of nitrogenous See also:matter, excrete an acid digestive secretion similar to that of the sundew, by means of which the body of the captured insect is digested and absorbed. After Darwin.

End of Article: SUNDEW

Additional information and Comments

There are no comments yet for this article.
» Add information or comments to this article.
Please link directly to this article:
Highlight the code below, right click, and select "copy." Then paste it into your website, email, or other HTML.
Site content, images, and layout Copyright © 2006 - Net Industries, worldwide.
Do not copy, download, transfer, or otherwise replicate the site content in whole or in part.

Links to articles and home page are always encouraged.

[back]
SUNDERLAND, ROBERT SPENCER, 2ND EARL OF (1640-17o2)... 		[next]
SUNDSVALL

Site © 2006 - Net Industries