CHLOROPHYLL AND GROWTH 123 



is inactive, or one side of this box may con- 

 sist of a sheet of blue glass which would 

 permit only the blue- violet rays to pass and 

 thus allow but a small amount of food to be 

 formed ; the plant may be grown in a substra- 

 tum, or nutritive solution, from which iron 

 salts have been omitted, and as a consequence 

 no chlorophyll would beformed in theleaves; 

 the shoot or the entire plant may be placed in 

 atmosphere made free from carbon dioxide b\^ 

 means of chemical reagents. Of these meth- 

 ods chief reliance is to be placed upon those 

 in which light is excluded from the plant, and 

 in which carbon dioxide is excluded from the 

 leaves. 



The former method induces such profound 

 disturbances of the chemical processes and 

 regulatory mechanism as to place the plant 

 under highly pathological conditions. The 

 more conclusive experiments are those b\' 

 which branches, or entire plants are intro- 

 duced into a sealed chamber, which is kept 

 free from carbon dioxide by means of solu- 

 tions of potassium hydrate, and the ventil- 

 ating openings were guarded with tubulures 

 similarly provided. The exact method of 

 dealing with the plant may be illustrated b\^ 

 the following description of the treatment of 

 A rissema triphyllum . 



The large tuberous corms were gathered 



