SUGAR: DIGESTION OF STARCH. 77 



with iodine. This experiment shows that sugar is formed in the leaves of 

 the Indian corn plant, but is changed to starch when stored in the seed. 



158d. Take several leaves of bean seedlings; test for glucose and cane 

 sugar as in i^Sc. Both are present. Test a leaf for starch. It is present. 



158e. Select a branch of sugar maple during autumn, winter, or spring, 

 about i cm. in diameter. From a portion scrape off all the bark so as 

 to remove all the color. Cut off some shavings of the white woody portion 

 and boil in a small beaker for one or two minutes. Filter and test for the 

 presence of both glucose and cane sugar as in paragraphs i^Sc and 1576. 

 Both are present (at least in several tests made in Decemb;r, 1906). The bark 

 is to be removed, since the coloring matter in it also reduces Fehling's solution. 



158/. Scrape some pulp from the inside of a sugar beet. Mix in dis- 

 tilled water in two test tubes. Test one for glucose and the other for cane 

 sugar. Cane sugar is present. 



159. How starch is changed to sugar. We have seen that in many plants 

 the carbohydrate formed as the result of carbon dioxide assimilation is 

 stored as starch. This substance being insoluble in water must be changed 

 to sugar, which is soluble before it can be used as food or transported to 

 other parts of the plant. This is accomplished through the action of cer- 

 tain enzymes, principally diastase. This substance has the power of act- 

 ing upon starch under proper conditions of temperature and moist. ire, 

 causing it to take up the elements of water, and so to become sugar. 



This process takes place commonly in the leaves where starch is formed, 

 but especially in seeds, tubers (during the sprouting, etc.), and other parts 

 which the plant uses as storehouses for starch food. It is probable that 

 the same conditions of temperature and moisture which favor germination 

 or active growth are also favorable to the production of diastase. 



160. Experiments to show the action of diastase. (a) Place a bit of 

 starch half as large as a pea in a test tube, and cover with a weak solution * 

 (about j per cent) of commercial taka diastase. After it has stood in a 

 warm place for five or ten minutes test with Fehling's solution. The pre- 

 cipitate of cuprous oxide appears showing that some of. the starch has been 

 changed to sugar. By using measured quantities, and by testing with 

 iodine at frequent intervals, it can be determined just how long it takes a 

 given quantity of diastase to change a known quantity of starch. In this 

 connection one should first test a portion of the same starch with Fehling's 

 solution to show that no sugar is present. 



(b) Repeat the above experiment using a little tissue from a potato, and 

 some from a corn seed. 



(f) Take 25 germinating barley seeds in which the radicle is just appear- 



* This solution of taka diastase should be made up cold. If it is heated 

 to 60 C. or over it is destroyed. 



