32 GAS EVOLVED. [CH. II 



descent electric light of 2 or 3 candle power may be used, 

 the intensity of illumination being easily varied by placing 

 the light at various distances from the plant. 



(43) Dependence on 00^. 



Transfer the plant to a beaker filled with water 



which has been boiled in the apparatus shown in fig. 4. 



After a time the water may be supplied with COa by 



blowing vigorously into it through a glass' tube. Repeat 



the observation with the stop-watch. 



(44) Temperature. 



Provide two beakers of water, one at a temperature 

 of 24°— 26° C, the other at 4°— 5° C. Place a specimen 

 in the warmer of the two and when the readings are 

 constant transfer it to the cold water. During the 

 experiment take note of any changes in the brightness of 

 the sky; if this precaution is forgotten it is easy to be 

 deceived by a passing cloud causing an alteration in the 

 rate of assimilation. 



(45) Chloroform. 



Repeat experiment 41 and add a small quantity 

 of chloroform-water, that is, of water in which not more 

 than 1 per cent, of chloroform has been shaken. If the 

 experiment is cautiously performed it should be possible 

 to seriously diminish the rate of gas-discharge without 

 killing the plant. 



(46) Coloured light. 



Proceed as in experiment 41, and when constant 



