RESPIRATION AND FOOD PRODUCTION 



25 



reason it was formerly believed that respiration, or the 

 absorption of oxygen by plants, took place only at night, 

 and some people were led to imagine from this that it is 

 unwholesome to have potted plants in a bedroom ; but the 

 quantity of oxygen absorbed by green plants is so small 

 as to be scarcely appreciable. 



While the leaf is the principal organ of respiration, this 

 function is carried on in other parts of the plant also, else 

 it could not survive during the leafless months of winter. 

 It goes on at all times, in all living parts, and the other 

 leaf functions also are carried on, to some extent, in all 

 green tissues. 



29. Relation of Respiration to Other Functions. — The 



functions of photosynthesis and respiration are mutually 

 complementary and interdependent, the one manufacturing 

 food, and the other using it up, or rather marking the activity 

 of those life processes by which it is used up. In this 

 respect it is strictly analogous to the respiration of animals. 

 The more we exert ourselves and the more vital force 

 we expend, the harder we breathe, and hence respiration 

 is more active in children than in older persons, and 

 in working people than in those at rest. It is just the 

 same with plants ; respiration is always most energetic 

 in germinating seedlings and young leaves, in buds and 

 flowers, where active work is going on ; 

 hence such organs consume propor- 

 tionately large quantities of oxygen 

 and liberate correspondingly large 

 quantities of carbon dioxide. 



Fill a glass jar of two liters' capacity 

 (about two quarts) with germinating 

 seeds, or with flower buds or unfolding 

 leaf buds arranged in layers alternating 

 with damp cotton batting or blotting 

 paper; close it tightly and leave it for 10.— Arrangement of 

 twelve to twenty-four hours. If the apPj"-^"\=. '° =how that 



■^ ^ carbon dioxide is given 



jar is then opened and alighted taper off by growing seedlings. 



