CHAPTER V 



PLANTS AND LIGHT 



Chlorophyll and Light. We have already learned that 

 the essential difference between plants and animals is 

 that plants can form their own organic food by means 

 of the light absorbed by the chlorophyll, while animals 

 have not this power. Carbon dioxid and water are the 

 substances from which the plant makes its food ; and the 

 first visible product of these in the plant is sugar or 

 starch. 



Value of Sugar and Starch. Sugar or starch is used in 

 forming all the different parts of the plant. Without 

 sugar or starch, no plant can grow, or even live. These 

 products are equally important to men, for it is to 

 secure one of these, or something made from it, that 

 every plant is grown in agriculture. As these products 

 are formed by the help of chlorophyll, and it is the leaves 

 the green parts of plants that contain the chloro- 

 phyll, we know that they are the parts where the sugar or 

 starch is formed. 



Light Essential. If we examine any cultivated plant, 

 we see that its leaves are arranged so as to receive all 

 the light possible. Since plants can form sugar (or starch) 

 only in the light, and have no value except when they 

 produce it, and in general are worth more, the more of 

 it they produce, it is very clear that good crops cannot 



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