CHAPTER III 



THE WATER-CONTENT OF PLANTS AND 

 THE GENERAL RELATIONS OF ROOT 

 SYSTEMS 



THE life and special activities of the plant or animal 

 are at all times conditioned by the water-supply. Plant 

 growth and production may be more sharply limited 

 within countries, regions, or localities by the water-supply 

 than by any other factor of the ordinary physical environ- 

 ment. A soil which does not receive and deliver to the 

 plant throughout the growing season a reasonably constant 

 supply is a sterile desert whatever may be the quality of 

 this soil with respect to latent mineral possibilities. 



Water is often regarded as a crude food-stuff, because 

 it enters abundantly into the composition of living things. 

 It does, in fact, contribute elements to the making of or- 

 ganic food, as shown later ; but for the moment it is most 

 important to consider water with respect to its solvent 

 action. All organic food-material presented to the living 

 cell must be in solution ; likewise the mineral nutrients 

 and the gases which take part in metabolism. Ordinary 

 plants are constantly in contact with a water-supply, 

 during their growing period, by means of special absorb- 

 ing surfaces. It is to be expected, therefore, that the 

 forms and functions of plants are to a considerable degree 



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