Page:Encyclopædia Britannica, Ninth Edition, v. 13.djvu/151

INSECTIVOROUS PLAN T S has an attractive, a conductive, and a secreting surface analogous to those of Sarracenia, but wholly different in histological details. The detentive surface is represented by the fluid secretion which is invariably present. This is developed before the pitcher opens, and has generally a FIG. 13. Darlinglonia caUfornica. faintly acid reaction ; it contains, as shown by Voelcker, malic and citric acids, together with chloride of potassium, and carbonates of soda, magnesia, and lime. Hooker proved the digestive powers of the fluid, even on substances Fio. 11. Pitcher of Nepenthes distillatoria. A, honey-gland from attractive surface of lid ; B, digestive gland from interior of pitcher, in pocket-like depression of epidermis, opening downwards ; C, transverse section of the samo. A, B, and C magnified about 100 diameters. so resisting as cartilage ; Rees and Will found that fibrin was dissolved even more rapidly by the secretion of the excited pitchers than in a test experiment with pepsin from the pig s stomach ; and Lawson Tait, Vines, and others have obtained the ferment in a separate state. Tait indeed finds two substances, both possessing great antiseptic powers, and both being apparently, together with acid, essential to digestion one a greyish-white precipitate with alkalies, which he terms "droserin," and which seems the analogue of pepsin; the other, "azerin," a transparent straw-coloured substance precipitated by alcohol, he com pares to ptyalin, the ferment of saliva. Droserin seems to be present in the secretion of all those insectivorous plants which possess the power of digestion, azerin perhaps in all without exception. The latter substance has the property of rapid deliquescence, so that it can only be preserved in hermetically sealed tubes, and its solution, like glycerin, quickly wets any body with which it comes in contact. A fly thrown into water never gets completely wetted, while one which falls into the secretion of any insectivorous plant is rapidly soaked and drowned by the fluid entering its trachea). Fio. 15. Cephalotus follicularis, showing ordinary leaves and pitchers, the right hand one cut open to show internal structure. Cephalotus. This plant bears ordinary leaves as well as pitchers. The latter somewhat resemble in general form those of Nepenthes, but are more complicated in histological details. Tait has proved the digestive action of their secretion. Morphology of Pitchers. Baillon, and indeed first of all Linnaeus, have pointed out how by exaggerating the con cavity of a peltate leaf like that of Nymphxa we obtain a pitcher of the type of Sarracenia. Intermediate forms are frequently shown by a variety of Piperomia arifolia. Hooker has given reason to believe that the pitcher of Nepenthes is not a transformed leaf, but a mere leaf- appendage answering to the water-secreting gland found at the end of many leaves. The apex of the leaf, instead of forming the lid as in Sarracenia, is represented by a filiform appendage (see fig. 16, F). Finally, Dickson has FIG. 16. Morphology of Pitchers. (Chiefly after Dickson.) A, ordinary leaf of Cephalotus ; B, monstrous leaf with spoon-shaped depression ; C and I), other abnormal forms more deeply pouched, showing formation of pitcher; E, ordinary pitcher of Cephalotus; F, pitcher of Nepenthes; G, pitcher of Sarracenia; a, apex of leaf. proved by comparison with monstrous forms that the pitcher of Cephalotus arises in a third and totally distinct way, by a calceolate pouching from the upper surface of the ordinary spathulate leaves, the lid here arising from the proximal side of the pitcher-orifice. Other Insectivorous Plants. Dischidia, an Asiatic genus