HEAT OF RESPIRATION 77 



portant. Further, a depression of the carbon dioxide output 

 is associated with succulent plants, hence in order to obtain a 

 figure representing a true measure of the activity of respiration, 

 the increase in organic acid content in addition to the gaseous 

 carbon dioxide should be determined. This aspect is con- 

 sidered by Maige and Nicolas,* who point out that in the 

 flowers they examined, the respiration intensity increased with 

 age when stated in terms of gaseous exchange, but showed a 

 decrease with age when measured in terms of wet and dry 

 weight. In the case of the gynaecium, that shows, as might be 

 expected from the activity of the contained structures, a real 

 increase with age, whilst the other parts of the flower exhibit 

 a decreasing respiration with age. 



With regard to the heat of respiration, it is easy to demon- 

 strate 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 barrow load of fresh lawn cuttings, especi- 

 ally if there is a good admixture of clover. Exact measurements 

 have been made by various investigators : Molisch f 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 4 7 C. was attained, the temperature again showed a fall to 

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

 maxima, 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 J found that in germinating 

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

 accumulated 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 



* Maige : " Rev. ge"n. Bot.," 1907, 19, i ; " Ann. Sci. Nat. Bot.," 1911, 14, i. 

 Maige and Nicolas : " Rev. ge"n. Bot.," 1910, 22, 409. 



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



Pierce : " Bot. Gaz.," 1912, 53, 89 ; see also Bonnier : " Ann. Sci. Nat. Bot.," 

 1893, 18, 12. 



