SOIL MOISTURE AND WILTING 133 



had no considerable effect upon the soil moisture content at the 

 time of wilting, providing that the wilting occurred under the same 

 general environmental complex under which the plants had been 

 grown. This proposition clearly supports the suggestion just 

 made, that, in order to bring out the remarkable relation between 

 the evaporating power of the air and the soil wilting point, it 

 is quite essential that the internal physical system of the plant 

 be not allowed much time for alteration. If the internal condi- 

 tions be allowed to change (as by a process of acclimatization) 

 or if they be differently established from the start (as by growing 

 plants under various external conditions), then, although the 

 plants may still seem alike to the eye, yet they differ markedly 

 in their physiological nature and are really different kinds of 

 organisms. By this consideration it is seen that what appears 

 to be a fundamental discrepancy between the conclusions of 

 Briggs and Shantz and those here expressed is probably not a 

 serious one, if it is a discrepancy at all. The problem treated 

 in the present paper is quite a different one from that attacked 

 by the authors just mentioned and the two conclusions may well 

 stand together. 



With the usual lack of uniform methods in physiological experi- 

 mentation in the hands of different workers, it is unfortunate 

 that no criterion for the quantitative comparison of the data here 

 given with those of Briggs and Shantz can be established. The 

 only physical analysis of the soil here used which was possible 

 at the Desert Laboratory in the summer of 1910 is far too crude 

 to be of value in comparing the soil mixture of these tests with 

 the soils of the Washington authors. Furthermore, their water- 

 holding capacities were determined with a soil column one centi- 

 meter high, while the determination mentioned earlier in this 

 paper was made with a 10 cm. column. Briggs and Shantz have 

 omitted any quantitative description of the aerial conditions of 

 their experiments, so that the atmometer data of the present 

 paper are of no avail for a common criterion. This is greatly 

 to be regretted, and it is to be hoped that workers in physiology 

 and ecology will eventually realize the importance of atmometric 

 records in specifically defining the aerial conditions under which 

 experiments are performed. 



