89 



than when calcium sulphate alone is added. On the other liand, the 

 presence or absence of calcium carbonate appeal's to have no effect 

 upon the neutralizing value of calcium sulphate when added to mag- 

 nesium chloride, sodium chloride, or sodium carbonate. 



An interesting comparison is that of the soluble salts, one with 

 another, in respect to their degree of toxicity in pure solution on the 

 one hand, and in the presence of an excess of calcium sulphate and 

 calcium carbonate on the other. It will be observed that the sequence 

 in the first column is ver}^ different from that in the second. The 

 most toxic salt or mixture is placed at -the head of each column. 



Table XL — Order of toxicity icith and icithout calcium salts. 



In pure solution: 



Magnesium sulphate. 

 Magnesium chloride. 

 Sodium carbonate. 

 Sodium •sulphate. 

 Sodium chloride. 

 Sodium bicarbonate. 

 Calcium chloride. 



In presence of an excess of CaS04 and CaCOs: a 

 Sodium carbonate. 

 Sodium bicarbonate. 

 Magnesium chloride.^ 

 Sodium chloride b 

 Calcium chloride. 

 Sodium sulphate. 

 Magnesium sulphate. 



a It has already been suggested that the limit in some of these highly concentrated solutions 

 containing an excess of calcium salts may bear some relation to the osmotic pressure of the 

 solution. It is thei-efore not a mere coincidence, perhaps, that the sequence in this column is 

 almost identical with that in Table II (of concentrations precluding any growth during the 

 culture). 



6 These two salts are equally 'toxic in mixtures if reacting weights be compared, while magne- 

 sium chloride is the more toxic of the two in parts of salt per 10<J,000 of solution. 



The interest and imx3ortance of the results obtained from the exper- 

 iments made with mixed solutions show the great desirability of 

 extending further this line of investigation. In fact, no aspect of the 

 work promises more substantial returns. An interesting problem 

 among the many which suggest themselves in this connection is that 

 of a possible relation between the degree of toxicity of a salt, alone or 

 in mixture, and the readiness with which it is taken up by the plant 

 from a solution. The occasion seems opportune to redirect attention 

 to a series of experiments made long ago by Wilhelm Wolf ^ as to the 



'Landw. Yersuchsst., 7, 193 (1865). The studies were made with a series of 

 sohitions. each of which contained two salts in equal amount. Combinations 

 were made with (1) salts of the same acid, but of different bases; (2) salts of 

 the same base, but of different acids; (3) with both base and acid different. In 

 each culture 200 c. c. of solution was employed, and after one-half of this volume 

 had been absorbed by the plant (allowance being made for the small quantity of 

 water evaporated directly from the solution) the amount of each salt taken up 

 with the water was estimated by analysis of the residual 100 c. c. of solution. 

 Young beans and maize were used in the e-xjieriments. Some of the results 

 obtained were as follows: 



From three mixtures, each containing 0.05 grams of each two salts, the plants 

 absorbed in percentages of the original quantity of each salt supplied: 



From ammonium nitrate plus calcium nitrate. 92 per cent of the former and 94 

 per cent of the latter. 



From ammonium nitrate plus magnesium nitrate, 92 per cent of the former and 

 86 per cent of the latter. 



From magnesium nitrate plus calcium nitrate, 74 per cent of each. 



Potassium nitrate was taken up from all combinations with other nitrates 



