XII] QUANTITIES OF OXYGEN CONSUMED 127 



the properly illuminated chlorophyll-corpuscles seize and 

 decompose carbon -dioxide is very great, and so some is 

 sure to escape the potassium-hydrate for a time. 



The best direct proof of the respiration of leaves in 

 daylight, however, is that furnished by experiments which 

 show that in an ordinary atmosphere, to which a little of 

 the vapours of ether and chloroform are added, respiration 

 proceeds normally, whereas the anaesthetics mentioned 

 inhibit the chlorophyll-function. 



The volume of oxygen consumed by green leaves is 

 never less than that of the carbon-dioxide evolved, though 

 it is very often found to be a little more : in very many 

 cases, nevertheless, the volumes of oxygen absorbed and of 

 carbon-dioxide given off are equal, or so nearly so that the 

 difference may be neglected. 



But in one and the same plant, under like conditions 

 of temperature, &c., the energy of respiration differs in 

 leaves of different ages : in the wheat, for instance, the 

 young leaves gave 0'6 vol. of carbon-dioxide for every 

 volume of oxygen absorbed, whereas the adult leaves 

 evolved an equal volume of carbon-dioxide for every 

 volume of oxygen consumed. Moreover the ratios differ 

 at different seasons of the year, being greater in the 

 spring and early summer than towards the end of the 

 year. 



Following the general law of respiration, that of the 

 leaf also increases in intensity as measured by the quan- 

 tities of oxygen consumed in equal times as the tem- 

 perature rises to 40 C., or thereabouts ; and the total 

 results vary also with the intensity and kind of light, 

 as also with the nature of the plant itself. 



