LATEX. The name, Latex, was first ap plied to certain plant juices which have a white, milky appearance. The white juice of the common milkweeds (Asclepias) is a familiar and typical example. The applica tion of the name was then extended to cover similar juices which lack the whitish appear ance, like the colorless, slimy juice of the Spider Lily (Tradescantia).
The latex is contained in cells which are often remarkable for their length and com plexity. In many families of plants, like the Asclepiadacece (Milkweeds) and Euphorbiacece (Spurges), the latex cells are differentiated early in the development of the embryo and continue to grow as the embryo develops into the seedling and into the mature plant, and may finally reach a length of many yards. Conse quently, they are the longest cells in the plant kingdom. They may branch profusely, but no transverse partitions are formed and, therefore, they are regarded as unicellular vessels. A portion of a single latex cell is shown in Fig. 1. The walls of latex cells are generally smooth and thin and more or less elastic. During growth, they weave in and out among the other cells but do not penetrate them. A small portion of a latex cell surrounded by other cells is shown in Fig. 2.
Not all of the latex carrying structures are formed in the way just described, for the partitions in rows of cells may become dis solved, so that long vessels are formed, the process being like that involved in the forma tion of the woody vessels which carry ordinary sap. Whether formed from a single cell or from rows of cells by the breaking down of partitions, long continuous tubes are developed. If there were any transverse partitions, they would interfere with the free flowing of latex.
The contents of the latex tube or vessels are as varied as the plants which contain them.
There is a rather thin layer of protoplasm lin ing the wall and containing many nuclei and various inclusions, while the hollow part of the vessel contains most of the latex. The consistency of the latex varies, but it is usually a milky sap which flows easily. It contains mixtures of gums and resins, rubber, fat and wax in emulsion. Sometimes there are tan pins, salts, ferments and poisonous alkaloids. In the Euphorbiacece there are also starch grains. Rubber is such an important form• of latex that it is treated under its own heading. The great Euphorbia trees of South Africa, when cut into with an ax, exude great quanti ties of a sticky, milky latex which•might be of commercial importance.
When a plant containing latex is injured, the latex flows out and quickly coagulates as it is exposed to the air. The latex of Euphorbia splendens, a plant very common in the cactus rooms of greenhouses, will pull out into threads as fine as cobwebs, within a minute from the time the cut is nine; in such a small plant the elastic material is not in sufficient quantity to be of any commercial value. In 'some plants, especially in the flower clusters, the latex tubes are very close 'to the surface and the tissue covering them is very thin and deiicate, so that creeping insects break -through and are held by the rapidly coagulating latex and thus prevented from reaching the nectar, which is reserved for flying insects which can effect cross-pollination. Consult Molisch, H., 'Studien Tiber den Mikhsaft and Schleimsaft der Pflanzen' (1901). Various textbooks on botany have paragraphs on latex.