No. 510] PROBLEMS IN PLANT ECOLOGY 375 



found any adequate method of interpretation by which 

 the data of the physical analysis may be made to aid in 

 the explanation of vegetational conditions. There is no 

 doubt that these data contain much valuable information, 

 if we but knew how to interpret them. 



A beginning has been made in the important and funda- 

 mental 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 even more dense than 

 that concerning the normal physiology of the roots them- 

 selves. 



The geological origin of soils (a subject which makes 

 up a large portion of the text-books on soils) is of no 

 possible importance in either agriculture or ecology. 

 Mitscherlich— the author of the most scientific book on 

 soils which I have come upon— says in his preface, 



For our cultivated plants the geological origin of the soil in which 

 they grow is in no way important; the growth of the plants must 

 always depend upon the /trrsrnt physical and chemical constitution of 



Of course this is just as true of uncultivated forms. 

 But attention needs to be called here to the principle 

 already mentioned, 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 enlightening results have 

 come from such comparisons, as, for example, those ob- 

 tained by Dr. Cowles and his associates in this field. 



The possible importance of small amounts of organic 

 chemical substances in the soil has been strongly empha- 

 sized by the work of the Bureau of Soils and by that of 

 Dr. Dachnowski and others, 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 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- 



