Problems of Physiological Plant Ecology. 45 



of general ecological problems in certain regions. For this 

 purpose the methods already at hand are perhaps satisfactory 

 enough, though we are unable to obtain automatic records of 

 fluctuations in these conditions. 



If the factors active above the soil surface present great 

 difficulties, those active in the soil present greater ones. What 

 knowledge has been gained by the agriculturists is seldom at 

 the disposal of the ecologist, partly, perhaps, from the nature 

 of the agricultural literature, and partly, perhaps, from a too 

 common feeling that agriculture and ecology are far apart. 

 But the agriculturists have not made very great progress in 

 this field. Their measurements of soil conditions are too often 

 merely determinations of the various amounts of inorganic salts 

 which can be extracted from the soil by one or another cleverly 

 chosen solvent. In some cases determinations are .made of the 

 total amount of organic matter in the soil, but it appears that 

 these chemical results lack much in ease of interpretation, so 

 much that they are of little value to the ecologist. Soils have 

 been classified by various workers according to the size of the 

 component particles, but I have not found any adequate method 

 of interpretation by which the data of the physical analysis 

 may be made to explain vegetational conditions. There is no 

 doubt that the data contain much valuable information, if we 

 but knew how to interpret them. A beginning has been made 

 in the important and fundamental inquiry into the attraction of 

 the soil for water and the ability of the soil to conduct water 

 to plant roots, but our ignorance in this regard is almost as dense 

 as that concerning the normal physiology of the roots themselves. 

 Attention may be recalled here to the principle already men- 

 tioned, namely, that in the pioneer work in such a field as this 

 it is often not well to analyze the great general factors to too 

 great an extent. Great general vegetational features may be 

 compared with great general soil features, and wonderfully enlight- 

 ening results have come from such comparisons, as, for exam 

 pie, those obtained by Dr. Cowles and his associates in this field. 



The possible importance of small amounts of organic chem- 

 ical substances in the soil has been strongly emphasized by the 

 work of the Bureau of Soils, and evidence in this regard is 

 rapidly accumulating from all parts of the world. There is now 

 little reason to doubt that bog soils and others which are poorly 



