8 



the effect of any one soil component. It is rare indeed that the 

 "alkali" is composed of but one salt or chemical individual. And, 

 as will be brought out later, it is entirely impossible to predicate 

 anything definite as to the action of a mixture of salts upon a plant 

 from a previous knowledge of the effects produced by each single salt. 

 Conversely, it is equally impossible to draw conclusions as to the action 

 of any one of a mixture of salts from observations of the effects pro- 

 duced by the mixture itself. 



The more exact methods of the laboratory are necessarj^ in order to 

 give us precise knowledge, and with this end in view the present inves- 

 tigation was undertaken. It is not claimed that the results so far 

 obtained are in all respects conclusive. The fact that only two species 

 of plants were employed in these first experiments is sufficient indi- 

 cation that they are not. In physiological research nothing is more 

 dangerous than generalization from the behavior of one or a few 

 species of plants to that of plant life as a whole. It is a well-estab- 

 lished fact that species differ widely in their reaction to a given 

 chemical or phj^sical condition. AVitness the fact that seaweeds will 

 thrive in water containing 1.5 to 3 per cent of sodium chloride, and 

 that salt marshes, whose soil is saturated with water containing nearly 

 or quite as much of this salt, often support a luxuriant vegetation, 

 while the average crop is killed bj^ a much more dilute solution of 

 sodium chloride. Certain plants show a marked aversion to limestone 

 soils, while other species are almost entirely limited to soils having 

 a high content of lime.^ But it is needless to multiply illustrations 

 of so familiar a phenomenon. 



That a similar diversity is manifested by different cultivated crops 

 in their sensitiveness to various mineral salts when present in the soil 

 solutions is well known. Therefore we can not safely predict, until 

 experiments with many different plants have been made, that the 

 order of harmf ulness of the alkali salts here established for two plants 

 will be found to hold for all or even man}^ of those which are com- 

 monly cultivated in the alkali regions. But, as it is obviously essen- 

 tial to the satisfactory prosecution of alkali soil work that a definite 

 standard for comparison of the salts be established, there need be no 

 further apology for the presentation of these first results of what it is 

 hoped will become an exhaustive investigation. 



In the progress of the work numerous data were accumulated which 

 appeared to possess a more than ordinary degree of scientific interest, 

 especially as relating to the chemical theory of the dissociation of 

 electrolytes in solution and to the recently published hypothesis that 

 various salts, or rather their dissociated ions, enter into compounds 



^ The interesting subject of " lime-loving" and " lime-avoiding " plants has been 

 much discussed by European botanists. It is synoptically treated by Drude 

 (Handbuch der Pflanzengeographie. p. 51) and by Schimper (Pflanzen geographic, 

 p. 105). The latter author gives an extensive bibliography. 



