CHAPTER X 



THE WORK OP LEAVES 



Certain plants reproduce themselves without seeds. 

 Some get along without stems. None of the important 

 higher plants, however, can exist without roots and leaves. 



64. Functions and Uses of Leaves. — Leaves are of 

 use to man as food, for the shade which they afford, and 

 for beauty. These benefits are incidental, however, to 

 the three functions which Nature has given them to per- 

 form. These functions are : 



First: to manufacture out of the water from the soil, 

 and the carbon dioxide from the air, starch for the plant. 

 This is known as photosynthesis} 



Second : to give off the surplus water taken in by the 

 roots. This is called transpiration. 



Third : to act as a storehouse for food. 



65. The Manufacture of Starch. — The phenomenon 

 of starchmaking takes place only in the green leaves and 

 green twigs of plants. Just how carbon dioxide, an 

 invisible gas existing in the air, can be made to unite 

 with water to form starch, liberating oxygen at the same 

 time, we can not say. Yet upon the fact that it does so 

 in the green leaves of plants, all life in the earth depends. 



' The term photosynthesis is derived from photo, meaning 

 light, and synthesis, the act of putting together. It means, then, 

 the act of putting together, or building up, by light. The 

 reaction is : 



6CO2 + 5H2O + Light = CsHioOs + 6 Oa 

 89 



