No. 545] PRESENT PROBLEMS IN SOIL PHYSICS 301 



3. The physical nature of the subterranean environ- 

 ment of terrestrial plants is effective in controlling plant 

 activities, mainly with regard to the possible rate of de- 

 livery of water by the soil to unit area of absorbing roots. 



4. It is highly desirable to study this power of water 

 delivery with reference not only to the growth of plants 

 but also to other soil characteristics, some of which are 

 already commonly measured. 



5. The whole problem of the physics of the subter- 

 ranean surroundings of rooted plants awaits the develop- 

 ment of an instrumentation which will not necessitate the 

 preliminary destruction of some of the most important 

 soil properties before the soil can really be studied. 



