^6 WHEAT RESISTANCE TO TOXIC SALTS. 



Magnesium clilorid, like the sulphate, seldom occurs alone in nature 

 in sufficient quantity to be of very gi'eat consequence. It is iiearly, 

 if not always, associated in the soil with some other salts, such as 

 those of sodium and calcium, which tend to neutralize its effect upon 

 plants. In these experiments with wheat, as in those wdth lupines, 

 it was found to i-ank next to magnesium sulphate as a toxic agent 

 when in pure solutions. 



The average limit of concentration of magnesium chlorid for 

 wheat seedlings is 0.00931 of a normal solution, as against O.OOTSG 

 for magnesium sulphate. Again, referring to Kearney and Camer- 

 on's results wdth the same salts for lupines, we find some variations. 

 As is easily seen wnth the writer's results with wheat, magnesium sul- 

 phate is only about one-third more toxic than magnesium chlorid, 

 while Kearney and Cameron's results show the suli3hate twice as 

 toxic as the chlorid. The investigators named found the roots of 

 lupines to barely survive in 0.0025 of a normal solution of mag- 

 nesium chlorid, while Kearney showed that Zea mays would live in 

 a solution a little more than thirty times as concentrated. Magne- 

 sium chlorid is twice as toxic to the wdiite lupine as to the least 

 resistant variety of wdieat tested, and six times as toxic to the lupine 

 as to the most resistant variety of wheat. It is a surprising fact that 

 some varieties of wheat are six times as resistant and that maize is 

 thirty times as resistant to this salt as Lupinus alhus: 



It will be seen that the variation of the wheat varieties among 

 themselves is more pronounced in the chlorid than in the sulphate. 

 While the toxic limit for the least resistant of the varieties is the 

 same (0.005 of a normal solution) for the two salts, that of the most 

 resistant variety (0.015 normal) is much higher in magnesium chlorid 

 than in the sulphate. The ratio of variation between the two ex- 

 tremes of resistance with magnesium sulphate was 2 to 1, as against 

 3 to 1 with the chlorid. 



