CONCLUSION AND SUMMARY 61 



the soil retarded the formation of the root system. This of 

 course is to be expected for there must be a most intimate 

 connection between the root and the medium in which it 

 grows. The very existence of the plant is dependent upon 

 its food supply as received from the air and soil and circu- 

 lated through the tissues by means of water received through 

 the roots. Under varying conditions of soil moistures such 

 as those in which the mesophyte finds itself it can not be too 

 conservative in the modification of its root system, and the 

 meager observations made indicate that our ruderal meso- 

 phytes have a root system which is varied directly with the 

 conditions of soil moisture and food supply. This is a most 

 interesting and fascinating subject for future investigation. 



III. CONCLUSION AND SUMMARY. 



A. WATER IN PLANTS AND SOILS. 



1. Water in Soils. 



The amount of physical water in soils varies directly with 

 their water-retaining capacity and the chief known factors 

 affecting the water capacity are gravity, capillarity, and 

 surface tension acting within the soil, and evaporation acting 

 upon the surface of the soil. 



The amount of physiological water m soils varies directly 

 with the amount of physical water held in the soil and in- 

 versely with the amount of hygroscopic water. The adapt- 

 ability and vigor of the plant varies its power to draw water 

 from the soil. The kind, quality, and texture of the soil and 

 the density of the soil solution are important variants in 

 determining the limit of physiological water. 



The amount of water in the soil non-available for the use 

 of the plant is dependent directly upon the ability of the 

 plant to withdraw water from the soil. The ability of the 

 plant is measured by its inherent nature as manifested in the 

 form of protective structures, by its adaptability to its chang- 

 ing life conditions, and by the vigor of its protoplasm. Soil 

 composition and soil texture affect directly the ability of the 



