USES OF THE PHOTOSYNTHETIC FOOD 273 



to catching insects. Plants with such leaves are often called 



"carnivorous plants " or " insectivorous plants." The " Pitcher 



Plants " are so named because the leaves form tubes or urns of 



various forms, which contain water, and to these pitchers insects 



are attracted and then drowned. (Fig. 245.) The plants known 



as "Sundews" have their leaves spread on the ground and 



clothed with secreting hairs. 



(Fig. 246.) These secre- 



tions not only entangle in- 



sects but digest them. In 



the "Venus Flytrap," por- 



tions of the leaves work like 



steel traps and hold the in- 



sects fast until digested. 



(Fig. 



Uses of the Photosynthetic 

 Food 



In plants, as in animals, 

 the chemical processes upon 

 which growth and other vital 

 activities depend are both 

 constructive and destruc- 

 tive. While the simpler ele- 

 ments are being transformed FIG- 247. Venus Flytrap, showing 



into complex substances, * he leaves which open and close in catch ' 



, , j.v . i ing insect? 



complex substances through 



respiration and other destructive processes are being broken into 

 simpler substances. These chemical transformations constitute 

 metabolism, and are said to be anabolic when constructive and 

 catabolic when destructive. Through the plant's metabolic 

 processes numerous substances are formed, of which protoplasm, 

 proteins, sugars, starches, fats, oils, hemicellulose, amino-com- 

 pounds, cellulose, wood, cutin, suberin, enzymes, acids, tannins, 

 glucosides, and alkaloids are common ones. All of these sub- 

 stances are thought to be of some use to the plant, although the 

 exact function of some of them is not definitely known. 



The photosynthetic grape sugar, since there is much evidence 

 that in most cases it is the chief food formed by photosynthesis, 

 may be regarded as a foundational food; for the photosynthetic 



