THE AMERICAN NATURALIST [Vol. XLIII 



drained soils contain similar substances. The ecologist 

 can not afford to neglect this important line of advance. 



The water conditions of the soil have not received the 

 attention which their importance justifies. For deter- 

 mining the amount of soil moisture our methods are con- 

 fessedly crude and unsatisfactory, yet they have not 

 been employed as extensively as their accuracy seems to 

 justify. Graphs of the fluctuations in the water content 

 have yet to be constructed, although their construction is 

 comparatively simple and their value for our purpose 

 must be very great. Such curves should replace the 

 bare and almost useless data of precipitation and run-off. 

 Improved methods of measuring soil moisture will of 

 course be of great value, if such can be devised. 



As to the rate at which the soil can supply water to 

 the plant— quite a different question from that dealing 

 with the amount of soil moisture— we know almost noth- 

 ing. This rate of possible supply, or the resistance 

 offered by the soil to water absorption by roots, is, I 

 think, perhaps at present the most important problem 

 in all ecology, and it has hardly been touched upon. 

 But the problems here suggested seem to be as difficult 

 as they are important. 



We know almost nothing in a quantitative way about 

 the relations between the oxygen of the soil and plant 

 development. If this field should be developed we should 

 undoubtedly be placed in condition to explain many dark 

 and complicated points. The capillary power of the 

 soil apparently determines, other things being equal, both 

 the rate of water supply and that of oxygen supply, and 

 perhaps the best that can be done here, in the absence 

 of more perfect methods, is to study plant behavior with 

 reference to capillary power and water content. But 

 ecologists have hardly even attempted to relate the easily 

 determined capillary power (which is constant in any 

 given soil) to the vegetation, and it is difficult to foresee 

 what important results might be forthcoming from such 

 a simple study. 



