LATEX (Lat., juice). The milky or colored juice which is found in special cells or tubes in plants, confined to eertain families of the angio sperms, namely the Papaveracea., Asclepiadace:e, Apoeynace:e, Eupho•biaeezp, Urtieace:c, Lobeli acea., Campanulacea., Ciehoriaceze, Aroidea., and 3lusacea'. The first eight families belong to the dicotyledons, and the last two to the monocoty ledons. Other monocotts contain mucilage vessel A, which agree in many features with the latex ves sels; the contents, however, lack the milky ap pearance, and are slimy. In most planto the latex is whitish or cream color; in the blood root. however, it is of a deep orange red, and in some other members of the poppy family of a lemon yellow. It is a watery fluid, containing many different substances in solution, and a considerable number in the form of minute drop lets or in the solid state, merely suspended in water. The latter fact gives to it somewhat the character of an emulsion, and probably promotes turgor (q.v.) of the latex-tubes. That they are highly turgid is shown by the fact that when a plant containing latex is wounded the juice ex udes promptly and in considerable amount. The dissolved substances are (1) salts, especially those of calcium and magnesium, varying much in relative amount and character in different species; (2) sugars, gums. and other carbohy drates; (3) proteids; (4) tannins, alkaloids, enzymes, and various waste products. The sub stances held in suspension are (1) minute gran ules of gums, resins. and caoutchoue; (2) oils; and (3) tannins, the two latter in the form of fluid droplets. Other substances, such as starch grains, proteid grains and crystals, oil-drop:, etc., are imbedded in the protoplasm with which each tube is lined (see below).
The latex-vessels are of two distinct kinds, (1) articulated and (2) non-articulated. The articulated tubes arise from the early fusion of rows of cells by the partial or complete absorp Lion of their end walls. A row of cells extend ing sidewise may fuse with the main line and so form side branches; or. outgrowths may arise from the main tube. penetrate between the adja cent cells, and finally fuse with a neighboring tube. The articulated latex-vessels, therefore,
are distinguished not only by their irregular out line, in which the mode of origin may be traced, but also by the numerous branches connecting with one another, and so forming a network. (Fig. 1.) The non-articulated vessels arise in the very young embryo through the difIcrentiation of meristem tissue. The cell: destined for latex tubes elongate, grow, and branch as fast as the neighboring tissue grows. and push their way almost independently among the adjacent young cells. While they branch abundantly.the branches do not join others and form a network as the articulated tubes do. They are distinguished by their smooth contour, often thick walls, and the absence of anastomosing branches (Fig. 2). The latex-vessels extend through the whole body of the plant, standing in close relation to the nutri tive tissue of the leaves on the one hand (Fig. 3) and the growing regions on the other. In the older parts of the stem they arc most abundant in the cortex and the They may be con sidered as a special form of conducting tissue by means of which the various foods contained in the latex are readily distributed from regions of manufacture or storage to the regions of use. When rich in food substances the latex is very opaque, becoming more translucent as the food diminishes. '.rhese variations in the food con tent of the latex are found to be parallel with the nutritive necessities of the plant. The latex-tubes arc lined with a delicate layer of protoplasm, in which are embedded the various special organs, nuclei of peculiar form. starch formers (leucoplasts, qx.). oil-formers (elaio plasts), etc. The latex itself lies within this protoplasmic body, occupying the same position as the cell-sap in an ordinary cell. The latex, therefore. may be looked upon as corresponding to the cell-sap which is present in every active cell, from which it differs only in the abundance and nature of the dissolved and suspended ma terials. Economically, the most important sub stance in the latex is caontehoue. which after manufacture constitutes the rubber of commerce.
See HU WIEN.