NUTRITION. 153 



water. A considerable amount of food is used to repair the 

 necessary destruction in respiration. A plant which is not 

 taking in food from without, or making food, is decreasing 

 constantly in (dry) weight through respiration. Respiration 

 and other destructive chemical changes incident to work re- 

 sult in the formation of a great variety of products called- 

 waste products because they take no further part in the pro- 

 cesses of repair or growth. 



