CHAPTER XIV. 

 NUTRITION. 



160. Bepair and growth. — Since the body of every plant 

 is constantly wasting away by reason of its own activity, it 

 is necessary that it should be as constantly repaired. It 

 must also, for a considerable time or throughout its whole 

 life, be furnished with material which can be used in the 

 making of new parts. Without an adequate supply of food, 

 therefore, neither repair nor growth is possible. To under- 

 stand what materials are necessary for repairing waste and 

 forming new parts of the living plant, the constituents of a 

 plant may be determined by chemical analysis. 



161. Chemical composition. — The greater portion of the 

 weight of every plant is found to be water. Of the firmer 

 parts it forms as much as 50 per cent, while of the softer 

 parts it may form 75 or even 90 per cent. The most watery 

 portions of some plant bodies, such as the juicy portions of 

 fruits and the whole body of the algae, may contain only 2 to 

 5 per cent, of solid matter. 



If the solid matter left after driving off the water at a temperature of 

 1 10° C. is burned, there remains a white material which crumbles under 

 pressure, the ash. The dry matter consists chiefly of three elements, 

 carbon, hydrogen, and nitrogen. The most abundant element in 

 addition to these is nitrogen. When the dry substance is burned 

 these four elements are driven off in gaseous form. An analysis of the 

 ash reveals the presence of sulfur and phosphorus in considerable amounts, 

 and also smaller quantities of the following elements: calcium, magne- 



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