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TEXTBOOK OF PLANT PHYSIOLOGY 



tion in different plants and in different parts of the same plant. 

 Respiration is closely connected with growth, and, therefore the 

 greater the energy of the latter, the higher is the respiratory rate. 

 Rapidly growing organs, whose cells are rich in protoplasm, often 

 respire more intensely than do animals. Thus man, for instance, 

 produces in 24 hr. a quantity of carbon dioxide weighing about 1 

 to 2 per cent of his body. The respiration of germinating seeds at 

 a temperature of 37° C. is of the same intensity. Still greater is the 

 respiration of molds, which produce as much as 6 or even 10 per 

 cent of carbon dioxide in 24 hr. per unit weight. 



Fig. 101. — Pettenkoffer*s apparatus for quantitative determination of carbon 



dioxide eliminated in respiration. The germinating seeds are placed in U-shaped 



tubes connected with cylinders, containing soda lime and absorbing CO2 of the air. 



The air current proceeds from right to left {after Palladin). 



The following table gives an idea of the quantity of carbon 



dioxide which is liberated by various plant organs during 24 hr. at 



room temperature per 1 g. of dry weight. 



Cubic Centimeters 



Full-grown leaves 12 to 24 



Growing rootlets 40 to 80 



Buds of trees 35 to 70 



Germinating seeds 60 to 120 



Growing mycelia of fungi 270 to 1,800 



The respiration of flowers, especially when unfolding, is as 

 intense as that of germinating seeds. 



The object of respiration in plants is the liberation of energy 

 for use in vital processes. Because of their enormous surface and a 

 comparatively low rate of respiration, it is impossible for plants 

 to maintain a temperature at a higher level than that of the sur- 

 rounding air. But, when a considerable quantity of intensely 

 respiring plant material, such as germinating seeds, flowers, or 



