The Utilization of Foods 85 



touch each other. These spots were formerly thought to be 

 due to jarring ia transportation, but they are now known to 

 be caused by packing the peaches so closely that the air does 

 not have full access to all the fruit. The respiration of the 

 cells at . the points of contact is in consequence interfered 

 with, and these cells are suffocated and gradually die. Ships 

 with specially ventilated holds are used in importing bulbs 

 from Holland and fruits from the tropics. The building of 

 ventilated holds came as a result of the death of several men 

 who attempted to unload a cargo of bulbs from an unventilated 

 bottom. 



Assimilation. Another part of the food constructed by the 

 plant is used for repair and for building additional protoplasm. 

 A machine, if allowed to stand idle and uncared for, gradually 

 goes to pieces. The cell is a very delicate mechanism, built 

 of highly complex substances, and the protoplasm of the ac- 

 tive cell requires constant repair. The foods that most nearly 

 approach protoplasm in chemical composition are the pro- 

 teins. Naturally these are the foods most readily changed 

 into protoplasm and are the ones mainly used in the process 

 of assimilation. Assimilation may be defined as the process 

 through which the living protoplasm is repaired or new proto- 

 plasm built up by the use of foods. Assimilation takes place 

 in all living cells. 



Growth. The enlargement of plants or the development of 

 new structures is called growth. The fact about plant Hfe that 

 is most famihar to all is that when a live seed is planted in 

 the soil it germinates, and that from it there develops a seed- 

 ling which continues to enlarge for a longer or shorter time, 

 depending on the plant and the conditions of growth. The 

 period of growth may be a month, as in the radish in mid- 



