19 



RESULTS WITH PURE SOLUTIONS. 



CONCENTRATION MAXIMUM PERMITTING SURVIVAL OF THE ROOTS. 



By appljang the methods and tests outlined above it was possible 

 to determine with a reasonable decree of accuracy the limit of concen- 

 tration for each of the salts in pure solution in which the root tips of 

 3^oung seedlings of white lupine could just survive. It is believed 

 that, like conditions being maintained and the same plant in the 

 same stage of development being used, the limits will not be materially 

 altered by further experiment. Moreover, it is regarded as not improb- 

 able that the salts will be found toxic in about the order stated below 

 if other plants or other stages of growth of the same plant be tested 

 with them. The limit of endurance in a solution of each particular 

 salt will doubtless be higher or lower for different objects, but the 

 general sequence of harmf ulness should remain practically unaltered, 

 so far as the higher plants are concerned. Experience alone can 

 demonstrate the correctness of this assumjition. 



The limit of concentration permitting roots of white lupine to 

 retain their vitality during twenty-four hours is, for each of the more 

 important readily soluble "alkali" salts, as follows, the limit being 

 stated both in parts of salt per 100,000 of solution and in fractions of a 

 normal solution : 



Table I. — Results of experiments with pure solutions. 





Name of salt. 



Degree of concen- 

 tration. 





Parts per 



100,000 

 of solu- 

 tion. 



Fractions 

 of a nor- 

 mal solu- 

 tion. 



Maprnpsinni snlphatfi 





7 

 12 

 36 

 53 

 116 

 167 

 1,377 



0.00125 



Magnesium cliloride Q ) 



0025 





.005 



Sodium sulphate (2) 



.0075 



Sodium chloride (^i) ~ 



.02 



Sodium bicarbonate (4) 



.02 



Calcium chloride 



.25 







Notes.— (1) With magnesium chloride the limit of endurance (for the whole plant), as deter- 

 mined byCoupiu [Rev. Gen. de Bot.. 10, 18« (1898)]. is 0.8 per cent, while with magnesium sulphate 

 the limit is 1 per cent, thus reversing the order of toxicity for the two salts as given above. 

 Wolfe (Landw. Versuchsst., 6, p. 2Uj notes the strongly toxic effect of magnesium solutions upon 

 roots of bean and maize. The brown coloration of the surface of the radicle, induced by these 

 salts, appeared a few hours after immersion. Wolf's suggestion that the very poisonous effect 

 of magnesium sulphate may be due to the decomposition of the salt by excretions of the roots 

 can not be regarded as possessing great probability. His experiments, which were designed 

 primarily to ascertain the volume of water absorbed by the plant from solutions of various salts 

 of different concentration, are considered by him to indicate that the cell wall [ectoplasm] is 

 less permeable to sulphates than to other salts (1. c, p. 217). Loew (Bui. No. 18, Div. Veg. 

 Phys.and Path., p. 42) foT>nd that Spirogyra died after four or five days of immersion in aO.l per 

 cent solution of magnesium sulphate, but remained alive for a long period in equivalent solutions 

 of sulphates of potassium, sodium, and calcium. Similarly a 1 per cent solution of magnesium 

 nitrate killed a smaller Spirogyra in six to twelve hours, while the nitrates of potassium, sodium, 

 and calcium, in solutions of corresponding strength, did not destroy the plant. The peculiarly 

 poisonous action of salts of magnesium described by Loew is explained by him on the hypothesis 

 that calcium forms intimate compounds with proteids. and that these ai e essential to the organ- 

 ization and life of the cell-nuclei and chloroplasts of the higher plants. Consequently, if mag- 

 nesium is supplied without calcium to plants, especially in the form of readily soluble .salts, such 

 as chloride, nitrate, and sulphate, the acids of the magnesium salts would be attracted by the 

 calcium which formed part of the nuclear proteid compounds. The latter would consequently 

 be disorganized, magnesium being unable to take the place of calcium in proteid compounds 

 without fatal disturbances of equilibrium in the cell. As evidence for this hypothesis is adduced 

 the corrective effect of the addition of lime to either soils or culture solutions in which plants 

 are suffering from magnesium poisoning, and the further fact that plants suffer less in culture 

 solutions from which both calcium and magnesium are absent than in such as contain magne- 

 ium but no calcium. It must be observed, however, that the chemical rationale of this theory 



