86 THE VEGETATIVE ORGANS 



portion add Fehling's solution ] and boil. Note the deep 

 orange colour produced. This reaction is characteristic of 

 grape-sugar. Test by the same means (i) the juice of the 

 Grape and (2) a few small pieces of Onion and compare the 

 results. Grape-sugar occurs abundantly in each case ; it is 

 of common occurrence in plant tissues, and is a valuable 

 and easily transported food. Now examine the starch 

 mucilage which has been acted upon by the saliva. Note 

 that the mucilage has dissolved. Test a small portion with 

 iodine solution. Is starch present ? As no violet coloration 

 results, we may conclude that the starch has been converted 

 into some other substance. To the remainder add Fehling's 

 solution and boil. What is the new compound formed ? 

 From this experiment we learn that saliva contains a 

 substance which has the property of converting starch into 

 sugar. Such a body is called a ferment or enzyme, and it 

 is by means of such ferments that we are able to digest 

 the starch present in our food. The starch-digesting ferment 

 in saliva is called ptyalin. Apply these tests to the solution 

 acted upon by diastase and compare the results. In this 

 case also the starch has disappeared. Diastase is a ferment 

 commonly present in plant cells, and it is by means of 

 such ferments that the insoluble starch grains are corroded 

 and disorganized, and finally converted into sugar. 



We have seen above that sugar is formed in green leaves 

 during sunlight. Part of this is converted into starch 

 grains within the cells of the leaf ; the rest is drained away 

 to the stem or other parts. In these organs it may either 

 (1) be converted into starch and stored, or (2) serve for the 

 nutrition of tissues that are growing. At night, when the 



1 Fehling's solution may be prepared and kept in two stock solutions 

 as follows : (1) dissolve 35 grammes of cupric sulphate in 200 c.c. 

 of water; (2) dissolve 70 grammes of rochelle salt in 200 c.c. of 

 a 10 per cent, solution of caustic soda. When required, make a 

 solution of equal volumes of 1, 2, and water. 



