AMOUNT OF CARBON DIOXIDE AND PHOTOSYNTHESIS 233 



even in the feeblest illumination and that it ceases only in abso- 

 lute darkness, while the increase of the illumination of some spe- 

 cies to sixty times the normal did not accelerate the process. 

 The intensity of illumination necessary'to affect the process has 

 not been accurately determined because of the difficulty in sepa- 

 rating the effects of the visible rays from the heat effects. 1 



299. Influence of Amount of Carbon Dioxide upon the Amount of 

 Photosynthesis. Secure some small leafy plant, or a shoot held in 



Fig. 116. Apparatus for generating carbon dioxide, connected with wash bottles. 



a flask of water and place it in the tubulated bell-jar described in 

 302, Fig. 118. Connect a carbon dioxide generator in action and 

 pass enough of this gas through a series of wash bottles and the 

 capillary tube of the bell-jar to raise the proportion of the gas in 

 the air of the bell-jar to 5 percent. The burette on top of the 

 bell-jar should be empty and open during the process. Close 



1 Ewart, A. J. On assimilatory inhibition in plants. Jour. Linn. Soc. 31 : 364. 

 1895-1897. 



