CHAPTER X. 

 THE PHYSIOLOGY OF PLANTS. 



1. Water plays an important part in the nutrition of plants. 

 It not only dissolves the mineral matters of the soil, which 

 constitute an important part of plant food, but it also con- 

 veys them into and through the plant. It is a constituent of 

 all vegetable material. In aquatic plants it may constitute as 

 much as ninety-five per cent, of the whole weight. In terres- 

 trial plants it generally averages about seventy -five per cent. 

 In consequence of this quantity of water the cells are rendered 

 turgid, without which growth would be impossible. If green 

 plants be dried in the air at ordinary temperatures, they lose 

 only a portion of their water. Thus Red Clover contains 

 seventy-nine per cent, of water, and when air-dry (as hay) it 

 contains seventeen per cent. Fresh pine-wood contains forty 

 per cent, of water, and the same, dry, contains twenty per 

 cent. The first quantity in each case may be called the free 

 water of vegetation. The second represents the water of organ- 

 ization. Only a very small portion of the water that is ab- 

 sorbed by the roots is decomposed and consumed in the 

 plant ; nearly all of it escapes from the surface of the leaves 

 and tender shoots. 



Select parts of various plants — especially succulent plants, and those that 

 contain much water, as growing Corn, Radish, Cucumhers, Watermelons, 

 etc. Cut them into pieces, and after weighing spread out in the sun or put 

 in a warm oven, till thoroughly dried. Weigh again and the difierence in 

 weight will be the amount of escaped water of vegetation. 



2. The transpiration (called also exhalation) or escape of 

 watery vapor from the surface of a plant cannot take place 



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