40 PRINCIPLES OF AGRICULTURAL CHEMISTRY 



be an essential agent in the decomposition of carbon dioxide and 

 the production of organic matter. Only those parts of the plant 

 which contain chlorophyll are able to assimilate carbon dioxide. 

 If, for any reason, chlorophyll is not formed, assimilation 

 cannot take place. The green color of chlorophyll is sometimes 

 disguised by the presence of other pigments. 



Effect of Color of Light. The effect of light depends upon its 

 color and intensity. The following are outlines of methods for 

 studying the effect of color of light on plants. 



(i) Plants may be grown in boxes of different colored glass. 1 

 This method allows the experiment to be continued any desired 

 length of time. The plants can be then subjected to analysis or 

 otherwise examined. The light which passes through colored 



Fig. 6. Tent for shading tobacco. Pennsylvania station, 

 glass, is not, however, usually a single color, but is admixed with 

 white or other colors, as can be easily seen by analysis of it with 

 a spectroscope. This is an objection to the method. 



(2) A ray of sunlight is decomposed with a prism and the 

 spectrum thrown upon a screen with a slit in it, allowing the 



1 Weber, Jahresber. f. Agr. Chem., 1875-6, p. 336. Flammarion, Exp. 

 Sta. Record 10, p. 103. 



