NATURE OF PLANTS 17 



is transferred to special parts of the plant, such as buds, roots, 

 seeds. Here it is stored as a reserve food to meet the needs of 

 the plant at such times as it is not able to manufacture food. 

 This transfer of foods is slow and consequently the rapidly con- 

 structed sugars gradually accumulate in the chlorenchyma during 

 the day. This would result in the saturation of the cells with 

 sugar and so stop the work of photosynthesis were it not for the 

 fact that the chloroplasts quickly change the sugar to insoluble 

 starch, thus leaving the cells free to receive more sugar. If 

 chloroplasts of well-sunned, starch-forming leaves are examined 

 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 



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. 



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- 

 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 

 3 



