320 MEMOIRS OF THE NEW YORK BOTANICAL GARDEN 



reaction has been accorded so much weight in these considerations 

 that natural floras have been classified in accordance with their 

 dependence on or antipathy for lime. In the case of the study 

 of the influence of the nitrogen-fixing powers of plants, on the 

 other hand, and their effects in the premises, a mere beginning 

 has been made. Such attempts therefore as have been made to 

 correlate natural floras with the soil conditions upon which they 

 are produced, have on the whole been obstacles rather than aids 

 to progress. 



It is well known to all of you that plant physiology has been 

 making great strides in its campaign against the unknown in 

 plant nutrition. Some of you may also be aware that the more 

 modern soils scientists employing the results of plant physiology 

 and those of physical and colloid chemistry have been able to 

 shed much light on certain hitherto mysterious manifestations in 

 plant growth and plant diseases. Their methods have consisted 

 in studying the effect not only of the qualitative nature, but 

 also of the balance between components and the total concen- 

 tration of the nutrient solution. Moreover, they have gained 

 some insight into the processes whereby colloids are enabled to 

 affect the foregoing factors very markedly as well as to affect the 

 available water supply. In addition, they have learned to study 

 the specific requirements of plants for forms of plant food materials 

 and these investigations have already yielded and will continue 

 to yield data of great moment in our approach to a more definite 

 knowledge of plant requirements and hence of the role played by 

 soil conditions in the cstal)lishmcnt of floras. In illustration of 

 these remarks, I may call your attention to the studies of Hutchin- 

 son and Miller and of Schreiner and his associates on the influence 

 of the form of nitrogen best suited to the nutrition of certain 

 plants, to Skene's work on the reaction of peat soils in relation to 

 characteristic floras there, and to the experiments of Stiles, Totting- 

 ham, Shive, McCall, Gile and others on the concentration of the 

 nutrient solution and its effect on i)lant growth. 



A consideration of such studies, and I have only adverted to a 

 few of them here, must impress the student of plants and soils 

 with their momentous significance for the future of our knowledge 

 of plant biology both pure and applied. Particularly for the 

 subject ininicdiatcly under consideration it would appear to the 



