46 AVHEAT RESISTANCE TO TOXIC SALTS. 



individual variation may be eliminated. Usually about ten days 

 of experiment and from GO to 100 seedlings were employed to estab- 

 lish the toxic limit for each variety in each salt. 



(3) Wheat is one and a half to six times as resistant as white 

 lupines, according to the salt used. In sodium bicarbonate the least 

 and in magnesium sulphate and sodium carbonate the greatest differ- 

 ence in resistance between these two plants is shown. • 



(4) Different varieties, representing the two extremes, vary in the 

 ratio of 1 to o in their resistance to the toxic effect of different 

 salts. This is especially true for sodium carbonate and magnesium 

 chlorid. In magnesium sulphate they vary in the ratio of 1 to 2. 



(5) The variety most resistant as a whole is not necessarily the most 

 resistant to every salt. The variety that averages least in resistance 

 may be twice as resistant to some one particular salt as that which 

 averages highest. In this fact may be found the secret of selecting a 

 variety for a locality where the soil contains an excess of some one 

 salt. 



(G) The least resistant variety is not always the least resistant for 

 every salt used. It may be exceedingly resistant to one or more salts 

 and yet have a very low sum total resistance. 



(7) It is not possible from the results with a few varieties to draw 

 general conclusions for all sorts of wheat. Each will have to l)e, 

 worked out for itself. 



(8) Varieties which come from localities where saline salts abound 

 are the most resistant in water cultures to these toxic salts. Varie- 

 ties from humid regions are less resistant. 



(9) In general, the more toxic the salt the greater is the ratio of 

 resistance of one variety to another. The less toxic the salt the 

 smaller is the ratio. For sodium carbonate and magnesium chlorid 

 the ratio of resistance is greatest, being as 1 to 3. For the remaining 

 salts it is smaller. 



(TO) Individual variation is more prevalent and makes the estab- 

 lishment of the toxic limit much more difficult in some varieties than 

 in others. 



(11) All the salts used act as stimulants in dilute solutions except 

 sodium carbonate and sodium chlorid. which were neutral even in 

 very dilute solutions. In some cases the elongation in dilute solutions 

 was nearly twice that occurring in the controls of hydrant water. 



(12) Absolutely pure distilled water does not hinder development, 

 but traces of zinc are sufficient to kill the root tips in twenty-four 



hours. 



(13) The economic importance of these results is based upon the 

 fact that water-culture experiments may be a means for saving seA'eral 

 vears of selection bv indicatina- whether a certain variety is adapted 

 to soil conditions in a particular region. 



