17° PLANT LIFE. 



crystallize | producing a crystalloid), and other materials are 

 frequently present, which form the globoid (fig. 175). 



237. Intracellular digestion. — When solid foods, insol- 

 uble in water, are to be moved from one part of the plant to 

 another it must be done by altering them into soluble sub- 

 stances. This is accomplished by means of enzymes of differ- 

 ent kinds, adapted to effect the alteration of various foods. 

 The most abundant enzyme is diastase, which has the power 

 of altering starch into a sugar called maltose. Enzymes fitted 

 to transform proteids are also found in considerable amounts. 

 When the foods have thus been brought into a soluble condi- 

 tion, they dissolve in the water present and move from one 

 part of the plant to another, chiefly by osmosis. As any 

 given material is used up in growth or repair, or is altered 

 into another substance, a constant stream of molecules of 

 this material moves toward the point at which it is disappear- 

 ing. Thus from the food sources it is transferred to the 

 reservoirs and stored in suitable form. Thence, when needed, 

 it is redissolved after digestion and carried to the active parts 

 which utilize it. 



F. Katabolism. 



238. Destructive changes. — Coincident with the processes 

 which result in the formation of complex organic substance 

 out of simpler ones are those which result in its destruction. 

 The constructive processes are grouped under the term anab- 

 n/i.xm, and the destructive ones are designated as katabolism. 

 In the green plants the anabolic changes predominate (be- 

 cause of extensive photosyntax), with the result that the plant 

 accumulates organic matter ; while in colorless plants kata- 

 bolic processes predominate, with the result that the plant 

 increases in bulk, but only at the expense of organic materials 

 previously existent. In all plants, however, both the con- 



