46 



The Plant World. 



drained owe the character of their vegetation in great part to 

 the presence in the soil of toxic bodies. There is evidence that 

 many well-drained soils contain similar substances. The ecolo- 

 gist can ill afford to neglect this important line of advance. 



The water conditions of the soil have not received the atten- 

 tion which their importance justifies. For determining the 

 amount of soil moisture our methods are confessedly crude and 

 unsatisfactory, but 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. Im- 

 proved 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 merely with 

 the amount of soil moisture — we know almost nothing. 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, 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 does not fluctuate in any 

 given scil, — to the vegetation, and it is difficult to foresee what 

 important results might be forthcoming from such a simple study. 



Finally, for a goodly number of ecological investigations, 

 the bacterial flora of the soil must be investigated. The agri- 

 culturists have made good progress here and we may do well 

 to follow them. The possibilities are very great. 



