CHIEF ENVIRONMENTAL CONDITIONS. 141 



concentration (intensity), but also with that of many others. The 

 general problem of the chemical relation of plants is, therefore, an 

 exceedingly complex one, so complex, indeed, that the problem of the 

 water or temperature relation becomes, by comparison, a very simple 

 matter. 



Upon the chemical relation of plants depends, in large measure, our 

 agricultural practice, and it is instructive to bear in mind the a priori 

 considerations of the above paragraphs when perusing the current 

 writings upon such questions as that regarding the use of fertiUzers, 

 for example. It is to be hoped that the succeeding developments of 

 plant ecology and of agricultural theory may be characterized by 

 greater cathohcity of perception than has prevailed in the past, and 

 that the forthcoming hterature may be burdened with less of that 

 familiar type of argument by which a single one out of many inter- 

 related conditions is enthusiastically proclaimed as the real and only 

 cause of some particular physiological phenomenon. 



There is much promise for the future in the study of chemical rela- 

 tions, however. The qualities of the chemical environment of plants 

 can already be quite readily determined; the identification of chemical 

 compounds is no longer a general source of serious difficulty, and we 

 are beginning to see some Hght in the darkness of our prolonged 

 endeavors to determine the intensities (concentrations, diffusion ten- 

 sions) of the various substances with which we have to deal. The 

 interdependence of the influences exerted by the various chemical 

 compounds occurring in the environment has recently attracted much 

 attention, and this bids fair to be an important way by which agri- 

 cultural theory may at length become physiological. Salt antagon- 

 isms — the influence of the presence of a certain concentration of one 

 salt upon the effect produced upon the plant by a certain concentra- 

 tion of another — were first brought into prominence by Loew\ and 

 are attracting much attention at the present time.^ 



3. CHEMICAL ENVIRONMENT IN NATURE. 



In a discussion of environmental conditions, Livingston^ has sug- 

 gested that perhaps the simplest and most obvious classification of 

 these promises most at the present time, and he divides these condi- 

 tions as a whole into those that are effective above the soil surface and 



1 Loew, O., Die Bedeutung der Kalk-Magnesiazalze in der Landwirtzchaft, Landw. Versuchs- 

 stat, 41: 467-475, 1892.— Loew, O., and D. W. May, The relation of lime and magnesia to 

 plant growth, U. S. Dept. Agric, Bur. Plant Ind. Bull. 1, 1901. 



2 Osterhout, W. J. V., On the importance of physiologically balanced solutions for plants,!!, 

 fresh water and terrestrial plants, Bot. Gaz. 44: 259-292, 1907.— Tottingham, W. E., A 

 quantitative chemical and physiological study of nutrient solutions for plant cultures, Physiol. 

 Res. 1: 133-245, 1914 (this paper contains many literature ref erences) .— Shive, 19056. 



'Livingston, B. E., Present problems of physiological plant ecology.. Am. Nat., 43: 369- 

 378, 1909. The same paper, with some omissions and modifications, appeared under the same 

 title in Plant Worid 12: 41-46, 1909. XC\V3 ' "^ '1 



/<5>' 



