114 RESPIRATION 



structures, a real increase with age, whilst the other parts of 

 the flower exhibit a decreasing respiration with age. 



It is easy to demonstrate by relatively simple means, due 

 precautions being taken against loss, that the evolution of 

 heat is a concomitant of respiration. The temperature 

 attained is cumulative, and a remarkable rise may result 

 which may be realized by thrusting the naked arm into a bar- 

 row load of fresh lawn cuttings, especially if there is a good 

 admixture of clover. Exact measurements have been made 

 by various investigators : Molisch * found that the bulked 

 leaves of Carpinus betulus reached a temperature of 51 C. 

 in fifteen hours, a fall then took place so that at the end of 

 forty-eight hours the temperature was 34 C. After the lapse 

 of one hundred and four hours a secondary maximum at 

 47 C. was attained, the temperature again showed a fall to 

 31 C. after one hundred and eighty hours. Of these two maxi- 

 ma, the first is an expression of the true respiration intensity 

 of the leaves, whilst the cause for the second is to be found in 

 bacterial activity. Pierce f found that in germinating peas 

 the greatest average gain in heat was 923-9 calories accumu- 

 lated in 23-5 hours, which is about equivalent to 8-55 calories 

 per minute per kilogram of peas, a measure roughly one 

 quarter less than the amount of heat given off by a mouse 

 under similar experimental conditions. It was further found 

 that the amount of heat liberated by germinating peas de- 

 creased with age. . 



Since respiration is a means of obtaining energy for the 

 needs of the plant, the evolution of heat represents excess of 

 energy and is a waste product, for which reason the temperature 

 of a normally respiring plant is not by itself a sure guide to the 

 amount or intensity of physiological combustion but rather 

 a measure of the inefficiency of the organism. 



STIMULATION. 

 The stimulation of the plant accelerates respiration, which 

 acceleration is marked by a rise in the output of carbon dioxide 



* Molisch : " Bot. Ztg.," 1908, 66, 211. 



f Pierce : " Bot. Gaz.," 1912, 53, 89. See also Bonnier : " Ann. Sci. 

 Nat. Bot.," 1893, 18, 12. 



