74 



POPULAR SCIENCE MONTHLY. 



dissolved in minute oil drops suspended in special masses of 

 protoplasm, as is the case with chlorophyll. 



Although this article is particularly concerned with the non- 

 green colors of plants, yet it will be necessary to outline the func- 

 tion and adaptations of chlorophyll, to which these substances 



- Synthesis. 

 Brightness. 

 Heat. 

 - Disintegration. 



Ked 



Yellow Green Blue Indigo Violet 



Fio. 



2. Corves showing Brightness and Synthetic, Thermal and Disintegrating 

 Effects of the .Regions of the Solar Spectrum. 



bear a special relation. Chlorophyll is perhaps the most impor- 

 tant coloring substance in the world, for upon this substance 

 depends the characteristic activity of plants, the synthesis of 

 complex compounds from carbon dioxide and water a process 

 upon which the existence of all living things is ultimately condi- 

 tioned. Only in a very few unimportant forms devoid of chloro- 

 phyll can the synthesis of complex from simple compounds or 

 from the elements be accomplished. The function of chlorophyll 

 may only be comprehended when its chief physical properties are 

 understood. These may be best illustrated if a solution of the 

 substance is obtained by placing a gramme of chopped leaves of 

 grass or geranium in a few cubic centimetres of strong alcohol 

 for an hour. Such a solution will be of a bright, clear green color, 

 and when the vessel containing it is held in such a manner that 

 the sunlight is reflected from the surface of the liquid it will 

 appear blood-red, due to its property of fluorescence, that of 

 changing the wave length of the rays of light of the violet end 

 of the spectrum in such manner as to make them coincide with 

 those of the red end. It is by examination of light which has 

 passed through a solution of chlorophyll, however, that the great- 

 est insight into its physical properties may be gained. If such a 

 ray of such light is passed through a prism and spread out on a 

 screen, it may be seen that there are several large intervals or 

 dark bands in the spectrum. The rays of light which would have 

 occupied these spaces have been absorbed by the chlorophyll, and 



