82 RESPIRATION 



takes place. The following figures, given by Matthasi,* 

 represent the mean value of carbon dioxide evolved by 2 grams 

 of cherry laurel leaf per hour at the temperature specified : 



5-8 C. . . -cooiCO 2 iS-2C. . . 



14-2 C. . . -ooo2jCO 2 257 C. . . -ooo6CO 2 



14-3 C. . . -ooo3CO 2 29-2 C. . . -ooo8iCO 2 



18-1 C. . . -ooo^CO 2 33-1 C. . . *ooi3CO 2 



The inspection of these figures shows that for the low and 

 medium temperatures employed there is a gradual increase in 

 the respiration activity. At higher temperatures variation 

 obtains and it was found that the respiration intensity rapidly 

 changed with the time of exposure and that leaves under 

 precisely the same external conditions gave varying results due 

 to some internal factor. This is illustrated by the following 

 results of certain experiments on isolated cherry laurel leaves 

 exposed to light and carbon assimilating. The respiration 

 values represent the carbon dioxide given off by 2 grams of 

 leaf per hour : 



38-3 C. . . -oo2oJCO 2 40-9 C. . . -ooi4CO 2 



38-3 C. . . -oo23CO 2 40-9 C. . . -ooi6CO 2 



42-9 C. . . -ooi5CO 2 



42-9 C. . . -0014002 



Also it was found f that the leaves of this plant in their 

 respiration exhibit the same relation to temperature as they do 

 in their carbon assimilation in that the initial value at higher 

 temperatures is not maintained but falls away, the higher the 

 temperature the steeper the fall. 



An increased temperature must be operative for some time 

 before the stimulation of the respiratory process is noticeable, 

 a sharp variation in temperature is without effect and a 

 change in the respiration intensity after transference from one 

 temperature to another is gradual.J 



Muller-Thurgau and Schneider-Orelli in their investi- 

 gation on the respiration of potatoes found much the same 

 phenomenon to obtain : mere variation in temperature effected 

 by heating and cooling is without effect unless the exposure to 

 the higher temperature be sufficiently prolonged. Potato 



* Matthsei : " Phil. Trans. Roy. Soc." Lond., B., 1904, 197, 47. 



fSee Blackman : " Ann. Bot.," 1905, 19, 281. 



J Blanc: " Rev. ge"n. Bot.," 1916, 28, 65. 



Muller-Thurgau and Schneider-Orelli : "Flora," 1910, 101, 39- 



