38 WHEAT EESTSTANCE TO TOXIC SALTS. 



resistance of imlividiial plants, and it. will be interesting to mention 

 a few of tlieni. In the experiments to determine the toxic limits for 

 the different varieties the resnlts were based on averages, e. g., in a 

 solution of sodium carbonate of a concentration that was taken to 

 represent the toxic limit 23 seeds Avere alive in a 0.01 solution and 27 

 dead. It is not known how many of those seedlings which were alive 

 miirht have survived in a solution still more concentrated, ]xn-haps of 

 twice the strength, nor is it knoAvn how many of those that were 

 killed would have been killed in a solution only half as concentrated." 



Instead of making tables to show the individual variation, as was 

 first suggested, only striking instances will be referred to under the 

 names of the dift'erent varieties. A series of tables would require 

 more space than can here be given to the subject. 



P> It (la pest. — In connection with the experiments wdth the Budapest 

 variety two striking instances have been noted, one with sodium 

 bicarbonate and the other with magnesium sulphate. The toxic 

 limits for these two salts are 0.025 and 0.01 of a normal solution, 

 resi)ectively. In one experiment, out of a number of seedlings in 

 0.015 normal sodium bicarbonate two died. In the case of magne- 

 sium sulphate, in one experiment all the rootlets were dead in 0.015 

 normal except one, which survived. Here are Iavo instances with 

 remarkable extremes. In the former case the two seeds w^ere of 

 exceedingly low vitality, while in the latter instance one seed had 

 remarkably great vitality. 



CJ,yl.—ko very marked individual variations presented them- 

 selves during the experiments with the Chul variety. 



Turl-ey. — Few remarkable variations were observed with the Tur- 

 key variety. But one instance deserves special attention. The aver- 

 age toxic limit in magnesium sulphate is 0.01 normal, but in a num- 

 ber of tests a few seedlings were readily killed in a solution only 

 half as concentrated as the solution in wdiich one-half of the total 

 number of individuals exposed to it survived. 



Preston. — The experiments with magnesium salts brought out two 

 interesting cases w'ith the Preston variety. The toxic limit for this 



a Moore and Kellenuan (Bui. 64, Bureau of Plant Industry. IT. S. Dept. of 

 Agriculture) have given some excellent instances of individual variability with 

 respect to resistance to toxic agents. They have made numerous experiments 

 with copper sulphate upon different alg;e which are found in water supplies. 

 They found that 1 part of copper sulphate to 2,000 of water was sullicient to 

 kill one-half of the individuals of Clilaiiiydomoiias pirifonitis exposed to it in 

 two days, while the same concentration was sufficient to kill only one-tenth of 

 the same form in three following days, and in three other days only one-fourth. 

 With DesmuHum swartzii 1 pa t of copper to 100,000 was sufficient to destroy 

 one-liajf nnd three-fourths, respectively, of the individuals involved in two 

 different sets of experiments. Numerous other instances might he cited, but 

 tliese will suffice to show that individual variation in this resi)ect is not c<.n- 

 tined to wheat alone. 



