SECEETION OF ENZYMES 455 



latter is readily possible. In the horse-radish and many allied 

 plants, the cells which form the enzyme do not themselves con- 

 tain any reserve materials, but are situated among those which 

 do, giving us as it were the starting-point of glands proper, whose 

 special function it is to secrete these ferments. In some of the 

 plants belonging to the Natural Orders Gapparidacece and 

 TropcBolacecB the glandular cell divides several times to form a 

 little mass or nodu.le of secreting cells, which must be regarded 

 as a rudimentary gland, though it is not provided with any 

 definite outlet or dud. 



In the seed of many grasses where there is a special organ, 

 the scuiellum, to effect the absorption of the nutritive material 

 of the endosperm and supply it to the growing embryo, the 

 outer layer of cells of this organ, called its epithelium, is a 

 very marked secreting structure, producing at least two enzymes, 

 which it discharges into the endosperm to effect the decompo- 

 sitions that must precede absorption. The tentacles of Brosera, 

 to which allusion has already been made, secrete an enzyme, 

 which, along with a weak acid, is present in the glairy matter 

 that they pour out over the captured insect. These tentacles 

 and the secreting structures of the leaves of Dionsea and other 

 plants, and possibly similar bodies in the pitcher of Nepenthes, 

 must be regarded as actual glands, comparable to those of the 

 animal body, though less complex in structure. Glandular 

 hairs, which consist of a few cells situated on a stalk, are found 

 in great numbers on other plants, especially some species of 

 Saxifraga. 



There are many of these enzymes present in different plants, 

 the function of some of which is stiU not understood. Many, 

 however, have been investigated with some completeness. They 

 are usually classified, according to the materials on which they 

 work, into four groups, viz. those which decompose respectively 

 carbohydrates, proteids, glucosides, and fats or oils. In nearly 

 every case the action is one of hydration, the body acted upon 

 being generally made to take up water, and to undergo a subse- 

 quent decomposition. 



Of those which act upon carbohydrates we have two varieties 

 of diastase, which convert starch into maltose ; inulase which 

 forms another sugar, levulose, from inulin ; inverfase, which 

 converts cane sugar into dextrose and levulose ; glucase, which 

 produces grape sugar from maltose ; cytase, which hydrolyses 

 cellulose, and pectase, which forms vegetable jeUy from pectic 

 substance occurring in the cell- wall. Of the second group pepsin 



