NATURE OF PLANTS 17 



in the afternoon, they will be found to contain minute glistening 

 bodies, the starch grains (Fig. 9, s) . The chloroplasts have the 

 power to absorb sugar and secrete starch. The construction of 

 sugars and their transformation into starch is effected with sur- 

 prising rapidity. If some plants of pond scum are placed in the 

 dark for twenty-four hours so that all sugars and starches may 

 be consumed, starch will re-appear in the cells in these plants in 

 from three to five minutes after their return to the light. Con- 

 sider the absorptions, decompositions, recompositions, and trans- 



c 



Fig. 9. Greatly enlarged chloroplasts from leaf of moss : a, plastid with 

 three starch grains, s; b, plastid elongating preparatory to division; c, d, 

 later stages in division. 



formations that have been effected in this short time. Is it 

 surprising that the exact nature of the changes effected in the 

 manufacture of foods is not known? It is evident as a result of 

 the rapid formation of sugar that starch must accumulate in 

 the plastids during the day. At night sugar is no longer formed 

 but the transfer of food continues as in the day. The insoluble 

 starch is now dissolved by means of a ferment or enzyme into 

 sugar so that by morning the cells are quite emptied of the sugar 

 and ready for another day's work. This accumulation and trans- 

 fer of foods can easily be demonstrated by cutting off in the 

 afternoon a leaf from clover, bean or other starch-forming plant 

 and placing them in alcohol. When blanched and tested with 

 iodine the blue or blue-black color shows that they have accumu- 

 lated a large amount of starch. Test in the same way leaves 

 taken from these plants early in the morning. No starch re- 

 action will be seen because the cells have been freed from their 

 starch during the night. The formation of starch is often used 



