9,^ WTTEAT RESISTANCE TO TOXIC SALTS. 



The writer does not claim that the limits thus fixed are absolute, 

 but lie believes that further experiments would change them very 

 little. To obtain absolutely exact results it would be necessary to 

 employ an indefinite number of solutions of intermediate concentra- 

 tion, and to make tests with a very large numl)er of seedlings. The 

 results recorded here, it is safe to assume, will answer all practical 

 purposes. The different sti'engths of solution of the same salt- dif- 

 fered from each other by 0.005 of a normal solution for sodium 

 chlorid, sodium sulphate, and sodium bicarbonate, and by 0.0025 of 

 a normal solution for sodium carbonate, magnesium sulphate, and 

 magnesium chlorid. That is to say, experiments were made with 

 solutions of a concentration of 0.015, 0.01. 0.005, etc., for sodijim 

 chlorid, sodium sulphate, and sodium bicarbonate, and of a concen- 

 tration of 0.01, 0.0075, 0.0025, etc., for magnesium chlorid, magne- 

 sium sulphate, and sodium carbonate, intermediate concentrations 

 being disregarded in practice. 



As mentioned earlier in this paper, the death point was determined 

 largely by the elongation of the roots beyond the point 15 mm. from 

 the tip, marked off by india ink. If the roots showed no additional 

 elongation the second 24 hours in hydrant water, they were considered 

 dead. In some cases, however, it has been possible to determine this 

 point by other means. 



In the case of the two magnesium salts a solution of a concentra- 

 tion considerably above the limit lilackens about 1 or 2 millimeters 

 of the root tip, and often causes the end of the root to bend in the 

 shape of a hook. An appearance of this kind is conclusive evidence 

 that the solution is much too concentrated. Both sodium carbonate 

 and sodium bicarbonate in very strong solution cause a yellowing 

 of the whole body of the root in the solution, and more or less loss 

 of turgor, due, doubtless, to plasmolysis. It is very seldom that 

 rootlets which show that condition at the end of twenty-four hours 

 in the solution will revive when placed in hydrant Avater. 



To make the results herein contained exactly comparable with those 

 furnished by Kearney and Cameron from their studies on lupines, 

 the toxic limits are given in this paper both in fractions of a 

 normal solution and in parts of salt per 100,000 of solution. In 

 addition, the mean of the limits of all the varieties is given under 

 each salt, so that a glance will show how much above or below this 

 point any particular variety may be in regard to each salt used. 



The salts have been found harmful in ])ure solutions in about the 

 order in which they follow each other in the succeeding jiart of this 

 report — that is. sodium sulphate is less harmful than sodium chlorid 

 when both aiv in equivalent concentration, and magnesium sulphate 

 is more harmful than sodium bicarbonate when in the same jiro- 



