1 66 General Botany 



Accumulation of food. A healthy plant usually manufactures 

 more food than it uses immediately, and this food may accumu- 

 late in various parts of plants. In the potato, surplus food passes 

 to underground stems, the tubers, where it accumulates. Tur- 

 nips and beets are examples of plants that accumulate excess 

 food in their roots. In the maple, the food accumulates in the 

 branches, trunk, and roots. In cabbage, food is stored in the 

 cluster of leaves at the top of the stem. In corn and cereals, 

 most of the food finally accumulates in the grain. In the century 

 plant, a considerable part of the excess food is stored in the thick, 

 fleshy leaves ; the process of accumulation may go on from 20 

 to 30 years, and the total quantity of food stored may amount 

 to many pounds. In nature such accumulated foods may be 

 used during the next season's growth of the plant or in starting 

 the growth of the offspring. 



When soluble substances pass into and accumulate in the cells 

 of the stem, they are largely transformed again into an insoluble 

 form. This makes possible the continued entrance of the soluble 

 material. For example, starch formed in potato leaves is trans- 

 ferred through the plant to the underground tubers in the form 

 of glucose and maltose, and there it accumulates in the cells in 

 the form of starch. It is beheved that the same enzyme which 

 changes the starch to maltose, under suitable conditions changes 

 the maltose back again to starch, and that in general the enzymes 

 that digest foods are the agents that under shghtly different con- 

 ditions build them up again into the more complex insoluble 

 forms. Enzyme activities may be reversed by changes of tem- 

 perature, acidity, and water content of the cell. 



Kinds of food accumulated. In any given plant in which food 

 is accumulated, protein, carbohydrate, and fat are all present. 

 Depending on the plant, however, the amount of any one of these 

 may be very great or it may be so small as to be practically negli- 

 gible. In the sugar cane and sugar beet the excess food occurs 

 mainly in the form of cane sugar (sucrose) . In the potato it is 



