55 



(10) The ameliorating effect of calcium suli)hate is much more 

 marked when it is added to sulphates of magnesium and of sodium 

 than when it is mixed with the corresponding chloride. It raises the 

 concentration limit endurable Ijy plant roots in magnesium sulphate 

 four hundred and eighty times, in sodium sulphate more than sixty 

 times. 



(11) Even i)lasmolysis, although supposedly a reaction to purely 

 physical stimuli, can apparently be completely i:>revented by altering 

 the chemical nature of a solution without materially diminishing its 

 osmotic i)ressure. At any rate, plasmolysis was not detected in cases 

 where a solid excess of calcium sulphate had been added to a 0.3 or 

 even 0.4 normal solution of magnesium sulphate, although a i)ure 

 solution of magnesium sulphate is verj' strongly plasmolyzing at 

 tlie concentrations named. 



(12) Calcium chloride appears to be peculiarly effective in neutral- 

 izing the effect of sodium carbonate. 



(13) The effect of one kind of ion in counteracting the physio- 

 logical action of another kind can not be entirely explained by a study 

 of the chemistry of the solution itself, but must in iDart be referred 

 to complicated changes in the i^rotoplasm of the organisms. The 

 theory that ions furnished by the dissociation of electrolytes form 

 intimate combinations with the proteids of protoplasm, and that 

 their mutually antagonistic effect expresses itself in a replacement 

 of one kind of ion by another as a result of change in the composition 

 of the surrounding solution, would api)ear to afford the key to this 

 problem. 



(l-t) At a certain degree of dilution all of these salts become 

 indifferent (i. e., neither toxic nor stimulating) in their action upon 

 plant tissues. The maximum concentration of the indifferent solu- 

 tion is likewise si:)ecific for each salt. 



(15) At a still greater dilution some of them, as the salts of calcium 

 and the two carbonates of sodium, produce a positively stimulating 

 etfect upon the growth of roots. 



(IG) Individual plants show a marked dissimilarity in their power 

 of resistance to the toxic action of the alkali salts. Such individual 

 differences are strikingly accentuated in solutions of sodium carbon- 

 ate and of sodium bicarbonate of the maximum concentration which 

 will permit any of the roots to retain their vitality. 



CONCLUSION. 



Too great stress can not be laid upon the fact that the experiments 

 upon which the i)resent report is based are merely ijreliniinary. 

 Furthermore, the}^ were designed primarily to afford a standard for 

 comparison of the salts involved. It is not to be expected — indeed, it 

 is assuredly not true — that in the soils containing these salts the con- 

 ditions are quite comparable to those maintained in the laboratory in 

 ^the course of these investigations. The physical nature of the soil, 

 s well as the presence of various other soluble substances, renders it 



