THE RELATION OF THE WATER CONTENT OP THE 



SOIL TO CERTAIN PLANTS, PRINCIPALLY 



MESOPHYTES 



By George G. Hedgcock 



introduction* 



A plant is either modified, or destroyed by its environment 

 whenever this is changed even in the slightest degree, and, 

 since the physical conditions vary constantly, a plant must 

 be an adaptive organism in order to meet all these require- 

 ments. Being originally an aquatic structure, in order to 

 become an intense xerophyte, it must have undergone a long 

 series of small changes in function and structure as it passed 

 over from the one type to the other. The mesophyte pos- 

 sesses a structure which prevents it from thriving in ex- 

 treme conditions of dryness or moisture. In periods of 

 drought it may adapt itself in a certain degree to dry condi- 

 tions, but lacking either a sufQcient store of moisture in its 

 tissues or the means of conserving what it has, it perishes 

 long before the true xerophyte. 



The mesophyte, since it grows in a substratum of soil, is 

 necessarily affected by the water content of the soil, and by 

 the varying conditions of soil moisture. In times of drought 

 it is quite noticeable that plants of one species die sooner 

 than others of a different species, and certain individuals 

 perish sooner than others of the same species, although 

 growing in the same soil plot. The observation of these 

 differences in the drought resistance of plants led to the ser- 

 ies of experiments the results of which are given in this pa- 

 per. Although the study has been made from an ecological 



•Accepted by the Faculty of the University of Nebraska as a thesis 

 for the degree of Master of Arts, June, 1901. 



