WATER SOILS. 759 



for all other cultivated plants if we knew more of the specilic roles of the different 

 elements of i)lant food and the comparative needs of plants in this respect. The use- 

 fulness of the method, however, is greatly impaired hy lack of exact knowledge of 

 the physiological needs and functions of plants. 



It is evident that useful results can he obtained by the method only when it is 

 employed under well-defined conditions, and the author offers the following general 

 definition: Physiological analysis of soil consists of two or more comparative syn- 

 thetic- cultui-al experiments, executed systematically with one or more species of cul- 

 tivated jilants, in a soil moilitied in various suitable ways by simple and cliemically 

 pure fertilizers, with the object of determining, on the basis of the examination of 

 the plants and the quantity, quality, and mineral comj^osition of the crops produced 

 the one or more necessary or useful fertilizing elements which are required by the 

 one or more species of plants experimented with, under the conditions of environment 

 in which the experiment is made. 



The author explains in detail how the conditions imposed l)y this definition may 

 be secured in experimental work. He classes experiments as complete and incom- 

 plete. The most simple incomplete analysis consists of two cultures, the one with 

 complete fertilizer, the other with the same fertilizer minus a single element, neces- 

 sary and indispensable or useful, to the experimental plant. The physiological 

 analysis is com{)lete when it comprehends at least the following cultures: (1) 

 Complete fertilizer, (2) complete fertilizer without phosphoric acid, (3) complete 

 fertilizer without nitrogen, (-4) complete fertilizer without potash, (5) complete ferti- 

 lizer without lime, (6) complete fertilizer without magnesium, (7) complete fertilizer 

 without iron, (8) complete fertilizer without sulphuric acid, (9) complete fertilizer 

 without common salt. For purposes of comparison a culture without fertilizer is 

 generally added. Projierly speaking, the latter is not at all a part of physiological 

 analysis. 



It is not only necessary to experiment with different kinds of plants, but to use as 

 large a number as practicable of individuals of the same kind. Comparison is made in 

 all cases with the culture receiving a fertilizer which is complete with reference to 

 the needs of the plant and the character of the soil, all the other cultures receiving 

 identically the same fertilizer, absolutely or relatively complete, with the exception 

 of a single fertilizing element. The importance of using only simple and chemically 

 pure fertilizers is strongly emphasized. 



The experiments must as far as possible be so made that the results may be inter- 

 preted in strict conformity to the method of difference. This, however, is an ideal 

 condition not realized in practice under present conditions of knowledge. The con- 

 clusions as to the effect of the fertilizers experimented with must be based upon (1) 

 the general aspect of the crops — height, color, resistance to parasites, to tendency to 

 lodge, etc.; (2) tlieir quantity; (3) their quality — richness in sugar or starch, flavor, 

 palatability to animals, etc.; and (4) their mineral composition — content of phos- 

 phoric acid, potash, etc. 



In discussing the value of chemical and physical examination as a means of study- 

 ing the productive capacity of soils, and as an adjunct to the method of physiological 

 analysis, the author says that, as a general rule, up to the commencement of the nine- 

 teenth century the most advanced agronomists occupied themselves almost exclu- 

 sively with the physical properties of soils. The biological laws, which control the 

 growth of plants, were for the most part unknown, and inexact, erroneous, or false 

 ideas were current regarding the causes which determine the fertility of soils. On 

 this point Liebig made the following observation in 1840: 



"It is very singular that our most distinguished, most capable agronomists have 

 taken so much trouble the last sixteen years to demonstrate that the soil conserves 

 all its fertility even when the fixed principles which it has lost are not restored to it. 



23461— No. 8—04 3 



