DIGESTION (Lat. digostio, from digercre, to digest I IN PLAN rs. The process by which foods are tendered tit for absorption, conduction, or assimilation (qq.v.). are sometimes soluble in water. or. when soluble. need to be altered to make them more readily diffusible or usable. Since no substances •nn be absorbed in solution in water, and since protoplasm and cell-•alls offer resistance to the movement of having large molecules, digestion is necessary.
'There are no special digestive organs in plants corresponding to the alimentary tract of animals, and voinparison mf leaves to the stomach is entirely misleading. Digestion may occur outside the plant body to make foods soluble and prepare them for absorption. Or it may °vein- in the interior of any cell of any organ. though it is most active in those cells which vmntain the largest quantities of foods that are to be rendered available for growth and repair. In both cases ig ae•omplished by the protoplasm. Doubtless the protoplasm may act directly, but in most eases it digests foods by secreting enzymes (q.v.) to
do the work. Enzymes may be produced in all the yells of all organ, e. g.. in leaves, tubers, the inyeelium of a fungus; or in certain cells, free of reserve food. e. g. nasturtium and other Cru eiferle: or in definite groups of cells constitut ing a gland (q.v.). e. g. garden nasturtium; or in a glandular epidermis. e. g. on the embryo of grasses; or in superficial glands, e. g. saxi frage and insectivorous plants. (See SECIIE. , TION.) Each prominent food is acted upon by a par ticular enzyme adapted to transform it. The follow ing table shows the principal 'sorts of plant foods. the enzymes by which they are digested, and the most important products formed.
CARBetlYDRATES Food Enzyme Produet $ . diastase.
ueNtrin Inulin . . inulase . cp./ow. .. a Ca riety of sugar S mad) . vertas, .
Maltose alnease glucose Pectins peel use peetie acid I1. PncerEms Albumins $ peptones and trypsin Globulins) I finally amides