22 PLANT LIFE 



of the sun, for its energy, reaching us through 

 the mediation of the plant, is the jons et 

 origo of our existence. How, then, does the 

 Chlamydomonas proceed by means of its 

 chlorophyll to make these more complex 

 food substances ? 



Although we are not as yet fully acquainted 

 with all the steps of the process, we already 

 know enough to enable us to sketch in out- 

 line the main sequence of events. Putting 

 the story in its simplest form, we may say that 

 the carbonic acid, which is formed when 

 carbon dioxide dissolves in water, is con- 

 tinuously broken up as the result of the action 

 of sunlight of a suitable intensity upon the 

 chlorophyll of the living plant. Oxygen 

 is liberated, and organic compounds, usually 

 sugars, are produced inside the cell. When 

 the reaction is sufficiently rapid, so that the 

 concentration of sugar reaches a certain 

 strength, starch often makes its appearance, 

 but it is merely a secondary product, depending 

 on the prior formation and accumulation 

 within the cell of sugar in sufficient quantity. 

 The earlier stages of sugar formation are still 

 obscure, but there is little doubt that form- 

 aldehyde (the formalin of commerce) is pro- 

 duced during the process. This substance has 

 been used as the starting-point for the synthesis 

 of sugars in the laboratory, and although it 

 is difficult to detect it with certainty in the 

 plant there are strong reasons for considering 

 that it really is formed as an intermediate 



