IMPORTANCE OF SUGARS 87 



tion although the carbohydrate reserve is greater ; thus after 

 a treatment over a period of forty hours, the leaves evolved 

 no more carbon dioxide* than they did after four hours. Such 

 observations indicate that a certain content of carbohydrate is 

 necessary, but an increase above this value, which is a vari- 

 able figure, is merely increasing the respirable capital of the 

 organ. 



Miiller-Thurgau and Schneider-Orelli * found that the 

 respiration of sweet potatoes is very high compared with 

 normal tubers ; in the autumn, when little if any sugar is 

 present, the respiration is low, but as the tubers increase in age 

 and sugar accumulates there is concurrently a more intense 

 respiration. According to Knudston f the respiration of the 

 vetch is intensified to different degrees by saccharose, glucose 

 and maltose, the last mentioned being less effective than the 

 others. Spoehr,+ from his investigations on the carbohydrate 

 economy of the Cactaceae, concludes that the rate of respira- 

 tion is not controlled by any one group of sugars, thus hexose 

 sugars, which often are considered to be of exceptional im- 

 portance in respiration, occur in the Cactaceae in variable 

 amounts under varying conditions of existence and sometimes 

 may be almost absent, but the respiration intensity is not 

 thereby reduced in any marked degree. Under conditions 

 which involve a poor supply of hexose sugars, the polysac- 

 charides are consumed in the respiratory processes and such con- 

 ditions are possibly connected with the formation of pentosanes. 

 The conditions referred to are temperature and water : a low 

 water content accompanied by a high temperature bring about 

 a decrease of monosaccharides and an increase of polysac- 

 charides and of pentosanes, whilst the contrary conditions, a 

 high water content and low temperature, are associated with 

 an increase of monosaccharides and a decrease of polysac- 

 charides and of pentosanes. 



With regard to the proteins, Palladin has shown that 

 during the germination of wheat in darkness the total protein 

 content and the soluble carbohydrates diminish whilst the 



* Muller-Thurgau and Schneider-Orelli, loc. cit. 



+ Knudston: " Cornell Agric. Exp. Sta. Mem.," 1916, 9, I. 



JSpoehr : " Carnegie Inst. Pub.," 1919, No. 287. 



Palladin; " Rev. ge"n. Bot.," 1896, 8, 225, 



