86 RESPIRATION 



nature of which is not clearly understood. Clausen * in the 

 case of seedlings and buds found the rate of evolution of carbon 

 dioxide to be about doubled with an increase of 10 C., and 

 Kuijper found the law to apply at temperatures between 

 o C. and 20 C. in the pea and wheat, and between o C. 

 and 25 C. for the lupin, the coefficient lying between 2 and 

 3 for a difference in temperature of 10 C. 



With regard to low temperatures, it is a well-known fact 

 that seeds, lichens, mosses, etc., especially when dry, retain 

 their vitality under exposure to intense cold ; even so low a 

 temperature as - 250 C. will not cause death. Since respira- 

 tion is in its complete expression a concomitant of life, the 

 process must continue in an attenuated form even at so low 

 a temperature as that of liquid air. 



FOOD. The continuance of respiration ultimately depends 

 upon adequate food supplies, and the intensity of respiration 

 may be much influenced by the presence of substances 

 immediately available as respirable material. Formerly it was 

 considered that sugar, more especially dextrose, was essentially 

 the respirable material, but no statement of general applica- 

 tion can be made. The action of foods in this connexion 

 varies with different plants and their physiological condition, 

 and is influenced by the operation of various natural internal 

 factors, such as acidity, which are not directly controllable in 

 experimental work. 



But notwithstanding this, general physiological experience 

 shows that carbohydrates are highly important in aerobic 

 respiration. Palladin,f for instance, found that 100 grams of 

 etiolated bean leaves, with depleted carbohydrate, gave off 

 102*8, 9 5 '9 and 70*2 mg. of carbon dioxide respectively 

 for three successive hours ; but after these leaves had been 

 grown in darkness on a solution of cane sugar for two days, by 

 which means their carbohydrate content was increased, the 

 rate of evolution of carbon dioxide was 152-6, 147*5, 146-8, 

 and 144*5 m g s - respectively for four successive hours. 



A more prolonged culture on cane sugar does not result in a 

 corresponding increase in the rate of carbon dioxide produc- 



* Clausen : " Landw. Jahrb.," 1890, 19, 893. 

 t Palladia : " Rev, gen. Dot.," 1893, 5, 449, 



