No. 495] CONSTANCY OF MUTANTS 



181 



of propagation is by cuttings or buds and hence only a 

 condensed individual life. It works in wheat, which seems 

 quite guarded in its closed or individual fertilization. 

 And it works in flax which, though usually self-fertilized, 

 is, no doubt, much given to intercrossing in the open. 



If the proofs rested only upon flax, where there are 

 many possibilities that open crossing might give rise to 

 the various Mendelian types, homozygotes, heterozygotes, 

 etc., the evidence might be thought to be thrown into 

 question, but even there, when crossing is promoted, 

 while there is every evidence of the occurrence of resist- 

 ant or non-resistant types among the crosses, resistance 

 is seldom found to approach the immune type upon the 

 first possible selection. In other words, if mutant- do 

 occur in flax through natural crossing or self-fertilization, 

 so far as our experiments are concerned, these resistant 

 forms are found to act exactly as do those which may he 

 developed from ordinary types of non-resistant flax. 



With this crop, one finds little, if any, resistance to 

 wilt and to rust in the best seed strains of southern 

 Russia or in the best seed strains from the new lands of 

 our northwest or in the best fiber strains of the disease- 

 free districts of northwestern Russia, though it often 

 crops out in the general seed samples from the worst 

 disease infection regions of central Russia. If mutants 

 were without cause and constant, one ought to find them 

 as readily in the seed of one district as in another. One 

 can, however, build resistance upon the least resistant 

 of these strains, if the work is started upon a graded 

 scale of disease infection which is increased year by year. 

 If the seed is placed under too heavy conditions of wilt 

 production, the plants are all killed in embryo or young 

 stages of growth and nothing is gained. If, however, 

 scrubs or runts may be saved from the first season under 

 weak disease infection and a graded infection is followed 

 thereafter, in approximately five years one may bring 

 these strains of seed to such a stage of resistance that 

 ordinary agricultural methods of cropping will maintain 



