SUMMARY. 19 



weight of salt per liter of solution, the minimum amount of calcium 

 sulphate necessary to effect the maximum possible neutralization, 

 as compared with the amount of the more toxic salt present in the 

 mixed solution, is about one-third in the case of sodium carbonate, one- 

 fifteenth in that of magnesium chlorid, and one-eightieth in that of 

 sodium chlorid. This is a strong indication that the neutralizing effect 

 is a physiological one, and that it can probably be satisfactorily 

 explained only when the composition and properties of living proto- 

 plasm are better understood. 



Prof. O. Loew and his students, in numerous papers dealing with 

 the "lime-magnesia ratio," have thrown much light upon the effect 

 of calcium salts in neutralizing the poisonous action of salts of magne- 

 sium. The physiology of the decrease in toxicity of salts of sodium 

 and magnesium brought about by the presence of a second salt, espe- 

 cially a salt of calcium, in the solution, was discussed by Kearney and 

 Cameron a in connection with Loeb's striking results with marine ani- 

 mals. Osterhout 6 has recently investigated this subject from the 

 point of view of Loeb's conception of a " physiologically balanced solu- 

 tion" and has shown that marine plants as well as marine animals 

 are very sensitive to pure salt solutions, but thrive in solutions con- 

 taining a mixture of salts, even when each component is present in an 

 amount that is toxic in pure solution. A mixture of the more impor- 

 tant salts present in sea water, each at about the concentration at which 

 it occurs in the sea, was found to be the best medium for the growth 

 of marine algas. 



The plants die much sooner in a pure sodium chlorid solution (isotonic with sea 

 water) than in distilled water. The poisonous effect of the NaCl largely disappears 

 if we add a little CaCl 2 . * * * In this mixture the plants live nearly as long as 

 in distilled water. Addition of KC1 to this mixture enables them to live longer 

 than in distilled water. Further addition of MgCl 2 and MgS0 4 enables them to live 

 practically as long as in sea water, c 



SUMMARY. 



(1) Different varieties of the same species, e. g., of wheat (Triticum 

 vulgar e), sorghum (Andropogon sorghum), and oats (Avena sativa), 

 differ considerably in their powers of resistance to the action of mag- 

 nesium and sodium salts in pure solutions. 



(2) Closely related species of the same genus, e. g., Egyptian and 

 Upland cottons ( Gossypium larbadense and G, hirsutum), show similar 

 differences. 



(3) Great differences exist between different plant species, even 

 when belonging to the same family, in tolerance of pure salt solutions, 



«Keport No. 71, U. S. Dept. of Agriculture, 1902, pp. 40 to 47. 



& Jour. Biol. Chem., 1:363 to 369, 1906, and Bot. Gaz., 42:127 to 134, 1906. 



cOsterhoutin Bot. Gaz., 42: 130 (1906). 



113 



