The Prevalence of Green Color in Plants 35 



there in photosynthesis any step requiring the doing of work, 

 and therefore the expenditure of energy? Our photosynthetic 

 equation supplies the answer, for it shows that the oxygen set 

 free has to be torn away from either the carbon or the hydrogen 

 of the carbon dioxide or water, as a necessary preliminary to the 

 union of the carbon with the remaining elements to form sugar; 

 and other evidence shows that the carbon dioxide at least 

 is thus dissociated. Now carbon dioxide is among the most 

 stable of natural compounds, which means that its constituent 

 atoms have an extremely strong affinity for one another, which 

 means in turn that ample power must be exerted to tear them 

 apairt. Most people know that in our laboratories water can be 

 separated into its constituent hydrogen and oxygen only through 

 action of an electric current (electrolysis), or of intense heat; but 

 carbon dioxide is even more difficult of dissociation. Here then, 

 in the preliminary dissociation of this very refractory substance 

 is that need for energy which we seek; and all the results of re- 

 search confirm this conclusion. Why it should be the red and 

 blue rays and no others which can do this work, we do not yet 

 know, nor yet precisely the way in which the chlorophyll applies 

 them to the task; but there is no question as to the facts. That is, 

 chlorophyll is a transformer of light energy into photosynthetic 

 work; and there j^ou have the explanation of its function in 

 plants, and the reason for its overwhelming prevalence in 

 vegetation. 



We can now summarize this part of our subject as another of 

 our botanical ver.ities, — the formation of photosynthetic sugar in 

 leaves requires first the dissociation of the refractory carbon dioxide, 

 which is effected by the energy of the red and blue rays of the sunlight, 

 applied to that work by the chlorophyll. 



It will perhaps contribute further to clearness if we summarize 

 the whole process of photosynthesis from another, and very human 

 point of view. The formation of the photosynthetic sugar, the 

 end of the whole process, is, after all, a manufacturing process 



