no RESPIRATION 



Spoehr and McGee * examined the effect of varying the 

 partial pressure of carbon dioxide on the respiration of leaves : 

 they found that when the amount of carbon dioxide is increased, 

 the amount of carbon dioxide emitted from the leaf is reduced 

 for a while and then rises to the original rate. Conversely 

 when the partial pressure of the carbon dioxide of the surround- 

 ing atmosphere is reduced, the rate of evolution of carbon 

 dioxide is increased for a time and then falls to the original 

 rate. 



These facts are of considerable importance, not only as 

 regards the economic aspect but also in their bearing on ex- 

 perimental work: results obtained for subjects contained in 

 closed vessels, as is not infrequent in experiments on respira- 

 tion, in which the products of the oxidative processes accumu- 

 late, may be an expression of the plant's activity not in a normal 

 but in a pathological condition and, therefore, may be value- 

 less. Further, a state of carbon dioxide anaerobosis may be 

 set up. 



INTENSITY. 



In general terms, the more active the body the more in- 

 tense the respiration, provided that the conditioning factors, 

 such as temperature, food, facility of gaseous exchange and 

 circulation in the plant, and so on, are favourable. Consider- 

 ing the plant as a whole, Bonnier and Mangin f recognize 

 two respiratory maxima in its seasonal development, the first 

 at germination, or on the unfolding of the leaf buds, and the 

 second at the opening of the flower buds. Ruby $ found that 

 the intensity of respiration was greater in leaves of young 

 than of old plants ; thus the amount of carbon dioxide evolved 

 per hour per gram of fresh weight of leaves from trees one 

 year old, three years old, and many years old was respectively 

 •200 c.c, -150 c.c, and -ioo c.c. In all instances the growth 

 period showed a one-and-a-half to two-fold increase in respira- 

 tion as compared with the non-growing periods. Nicolas § com 



* Spoehr and McGee : " Amer. Journ. Bot.," 1924, 1 1, 493- 

 f Bonnier and Mangin : " Ann. Sci. Nat. Bot.," 18S5, 5, 315. 

 J Ruby : id., 191 7, 20, 1. 

 § Nicolas : " Rev. gen. Bot.," 1918, 30, 209. 



