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THE AMERICAN NATURALIST [Vol. XL VI 



avoid this difficulty, but all are exceedingly cumbersome 

 in the operation and are at best of somewhat doubtful 

 efficiency. Here is suggested a line of work which has 

 already been attempted by a number of enthusiastic 

 students, many of whom have afterward given up in 

 despair without even publishing their experience. The 

 director of one of the great European experiment sta- 

 tions told me of a somewhat elaborate apparatus which 

 he once constructed for determining soil moisture in situ. 

 He concluded with the remark, "the principle was cor- 

 rect enough, but the method proved useless." I am sure 

 that he is not alone in his experience. But the problem 

 of soil instrumentation will not be dropped; I am confi- 

 dent that the future will develop methods in soil physics 

 which will not necessitate any alteration in the soil at 

 the time a determination is made. Studies upon the soil 

 properties in the light of their role in plant environment 

 and accompanying studies on the physics of plant activi- 

 ties will do much toward furthering our science in this 

 direction. The actual accomplishment of this end may 

 not be very far off; we may take heart from such facts 

 as this, that a single decade has sufficed to bring aerial 

 navigation from the limbo of scoffed-at impossibility (in 

 the minds of all but a very few scientists) into the cate- 

 gory of accomplished fact. And the importance of ade- 

 quate methods for the study of problems of the soil is far 

 greater, and probably will ever remain far greater, than 

 that of any problem of transportation. 

 To summarize my suggestions : 



1. The soil water relation is of fundamental impor- 

 tance if we are some time to know about and be able to 

 predict and control plant processes. 



2. The moisture of the soil, as well as its other fea- 

 tures, is most profitably to be studied as plant environ- 

 ment, the relations which obtain between plant activity 

 and soil phenomena comprising a fundamental and 

 primary requirement for the scientific advance of our 

 knowledge. 



