102 CIRCULATION AND USES OF FOOD BY PLANTS 



The greatest factor, however, is transpiration of water from 

 leaves. This evaporation of water in the form of vapor seems to 

 result in a kind of suction on the column of water in the stem. In 

 the fall, after the leaves have gone, much less water is taken in by 

 roots, showing that an intimate relation exists between the leaves 

 and the root. 



Summary of the Functions of Green Plants. — The processes 

 which we have just described (with the exception of food making) 

 are those which occur in the lives of any plant or animal. All 

 plants and animals breathe, they oxidize their foods to release 

 energy, carbon dioxide being given off as the result of the union of 

 the carbon in the foods with the oxygen of the air. Both plants 

 and animals digest their food ; plants may do this in the cells of 

 the root, stem, and leaf. Digestion must always occur so that food 

 can be moved in a soluble condition from cell to cell in the plant's 

 body. 



Plants with Special Digestive Organs. — Some plants have 

 special organs of digestion. One of these, the sundew, has leaves 

 which are covered on one side with tiny glandular hairs. These 



Leaf of sundew closing over 

 a captured insect. 



The Venus fly trap, showing open 

 and closed leaves. 



attract insects and later serve to catch and digest the nitrogenous 

 matter of these insects by means of enzymes poured out by the 

 same hairs. Another plant, the Venus fly trap, catches insects 

 in a sensitive leaf which folds up and holds the insect fast until 

 enzymes poured out by the leaf slowly digest it. Still others, 



