50 General Botany 



In photosynthesis In respiration 



Oxygen is released. Oxygen is' consumed. 



Energy is accumulated. Energy is released. 



Simple molecules are built up into Complex molecules are broken down 



complex ones. into simple ones. 



P'ants accumulate food and increase Plants consume food and decrease in 



in weight. weight. 



Comparative rates of respiration. The rate of respiration is 

 greatest where there is rapid growth, as in germinating seeds, 

 opening flowers, and ripening fruits. In some of these it is much 

 more rapid, bulk for bulk, than in animals. A man gives off in 

 respiration about 2.5 per cent of his dry body weight of carbon 

 dioxide every twenty- four hours. Actively growing parts of 

 plants, hke opening flower clusters, may give off 10 per cent of 

 their dry weight in the same time. Some kinds of germinating 

 seeds give off carbon dioxide equivalent to 30 per cent of their 

 dry weight in a day. The average growing herbaceous plant, 

 like corn, loses carbon dioxide at a rate not far from i per cent 

 of its dry weight per day. About one fourth of the food manu- 

 factured by an acre of corn is used in respiration. Thus a mature 

 plant contains only about three fourths of the carbon that was 

 absorbed in photosynthesis. Since photosynthesis takes place 

 only during sunlight, the average rate of photosynthesis in a 

 corn plant is how many times the rate of respiration? 



The lowest rates of respiration occur in dry seeds and other 

 dormant structures, and there is comparatively httle respiration 

 in woody stems and other hard parts in which there are only a 

 few living cells. 



Respiration of fruits and vegetables. How important is the 

 recognition of the respiratory requirement of living cells may be 

 illustrated by the difflculties that have been met with in storing 

 and shipping fruits and bulbs. Peaches, during shipment, some- 

 times develop brownish spots where they touch each other. 

 These spots were formerly thought to be due to jarring in trans- 



