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. 1 1 6. 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. 1 1 8. 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 per cent. 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. 



