RESPIRATION OF PLANTS 91 



The predominant role of the sugars in nutrition, as well as in 

 respiration, is, moreover, suggested by the interesting fact that 

 molds develop more slowly on fats than on sugars. The reason 

 of this is that fats must previously undergo a complex transforma- 

 tion, while sugars are utilized directly. The same is indicated 

 by the transformation, described above (Art. 17), of fats into 

 sugars during the germination of oily seeds. 



22. The Dependence of the Respiratory Intensity on the 

 Conditions of the Surrounding Medium. — Being one of the 

 manifestations of the vital activity of protoplasm, respiration 

 may be realized only within the limits of conditions of the sur- 

 rounding medium that will permit the existence of living proto- 

 plasm. All factors killing protoplasm Hkewise inhibit the normal 

 process of respiration. With some methods of killing the 

 protoplasm that affect less profoundly the structure of the hving 

 substance — e.g., killing either with chloroform vapor or other 

 toxic substances or by freezing — after the death of the cells, the 

 processes of oxidation and decomposition continue for some 

 time, and are accompanied by a liberation of carbon dioxide and 

 absorption of oxygen. These processes are of great theoretical 

 interest, for their study allows one to penetrate more profoundly 

 into the internal chemism of respiration. However, this is not 

 the normal process of respiration, and thus it does not stand in 

 contradiction to the general statement that respiration is insepar- 

 ably connected with life. 



Of the many factors affecting respiration, let us first examine 

 the influence of temperature. Temperature is an environmental 

 factor exerting an effect not only on all vital processes but like- 

 wise on those of a purely chemical oiature. According to the 

 rule of van't Hoff, the rate of a chemical reaction doubles or 

 trebles with each increase of 10°C. in temperature. This acceler- 

 ation of the reaction with an increase of 10°C. in temperature 

 is designated as the temperature coefficient and is represented 

 by the symbol Qio. The van't Hoff coefficient may be expressed 

 by the equation Qio = 2. The temperature coefficient, however, 

 is frequently more than two. 



It must be emphasized that vital processes follow van't Hoff 's 

 rule only in comparatively limited temperature ranges, between 

 and 30 to 35°C. With a further increase of temperature, the 

 acceleration slows down; then there follows rapid decrease in 



