Food'-making 



(The plant, of course, produces carbonic-acid gas 

 inside the cells themselves in breathing, but far too 

 little to supply its own needs in food-making. It 

 therefore draws upon that produced by animals and 

 by fires.) The process of food-making is a very 

 complicated one, but the first visible product is 

 starch. This is made from the water and the 

 carbonic-acid gas, the former being split up into its 

 constituent oxygen and hydrogen, the latter into 

 carbon monoxide and oxygen. The two oxygens 

 are no longer wanted and pass off into the air. The 

 carbon monoxide and the hydrogen are caused to 

 combine together to form sugar, which is further 

 changed to starch. 



To do this work of food-making power is wanted, 

 just as it is to do any other work. We have already 

 pointed out that a certain temperature is required to 

 enable any work to be done, but heat alone will not 

 supply the energy for doing this special work : the 

 only form of energy which can be used is derived 

 from sunlight or light containing similar rays. When 

 the rays of light fall upon a leaf they do not all pass 

 through it, but some are arrested by the green colour 

 which is so characteristic of foliage (it is present even 

 in purple leaves, such as those of the purple beech or 

 purple plum). The rays so absorbed are used by 

 the living stuff of the leaf as a source of power, and 

 only when light falls upon a green leaf can food be 

 made. Anything that interferes with the falling 



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