86 



THE VEGETATIVE FUNCTIONS OF PLANTS 



therefore, all insoluble stored foods must be converted 

 into soluble substances and dissolved. The process of 

 converting an insoluble food into a soluble substance and 

 dissolving it is digestion. This change, like the various 

 processes in photosynthesis, is brought about by various 

 enzymes, which have the power of converting insoluble 



Fig. 63. — Venus's flytrap {DioncEa muscipula). Insects are captured 

 by the rapid closing together of the two valves of the leaf-blade. When 

 the valves come together the rigid marginal teeth interlock, making escape 

 impossible. The digestive enzyme is secreted by glands distributed over 

 the surface of the valves. ^ (After John Ellis.) 



starch, proteins, and fats, into soluble substances. Starch 

 is converted by diastase (one of the earliest known enzymes) , 

 proteins by proteases, and fatty substances (lipoids) by 

 lipase. 



