84 



ELEMENTS OF GENERAL SCIENCE 



93. Sugar and starch in the leaf. Sugar is commonly 

 formed in the leaf in the process of photosynthesis and 

 is being continually carried away for use in other parts of 

 the plant. On a bright, sunny day it is made much more 

 rapidly than it can be carried away or used, and if there 



were not some way 

 to dispose of it the 

 sugar would accu- 

 mulate in the leaf 

 until the sap be- 

 came so rilled with 

 it that the work of 

 the leaf could not 

 go on. The leaf 

 has the power of 

 changing the ex- 

 cess sugar into 

 starch. This re- 

 moves the excess 

 carbohydrate from 

 the sap, since starch 

 is not readily dis- 

 solved in water. 

 By evening, if the 

 day has been a 

 bright one, a great 

 deal of starch is 

 stored in the leaf. 

 At night, when no sugar is being made, the starch in the 

 leaf is slowly changed into sugar by means of a process of 

 digestion. Some of it is used as food for the leaf and some 

 is carried away to serve as food in other parts of the plant, 

 to be stored more permanently as starch in seeds or roots 

 or to be converted into cellulose in the woody stem. The 

 stored food may be taken up and used at a later time. 



FIG. 43. Dodder a dependent plant 



The tangled, leafless vine is the dodder. It secures 



its food from the other plant, which is known as its 



host, while the dodder is a parasite 



