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THE AMERICAS' XATl'RALIsT [Vol.L 



indirectly in the formation of several different types of 

 mutated gametes. Many mutations are not concerned 

 with such obvious changes as the shifting of chromo- 

 somes, but seem rather to depend upon physico-chemical 

 and chemical alterations of the germ plasm. Obviously 

 some such alterations would result in physiological as 

 well as morphological mutations. Just as certain mor- 

 phological changes are not advantageous, or even dis- 

 tinctly harmful, so certain physiological changes might be 

 harmful and lead to sterility. Some premutations (and 

 by a premutation I mean the inauguration of an unstable 

 condition in the germ plasm) might be of such a nature 

 that the nutrition of the spore mother cells would be inter- 

 fered with. These might fail to develop, fail to undergo 

 the reduction division or might give rise to defective 

 daughter cells. 



Thus mutation, equally as well as hybridization, may 

 account for sterility. There are several groups of plants 

 in which sterility has apparently come about without the 

 possibility of hybridization. Perhaps Davis's genetically 

 pure CEnothera grandiflora, with perfect pollen, provides 

 a case of hybridization without subsequent mutability. 

 Those who assert that germinal instability comes about 

 only by hybridization can bring forward no proof of their 

 assertion. Conversely, the mutationist can not prove 

 that any plant in existence has had an unmixed ancestry. 

 The most that he can do at present is to show that muta- 

 tion takes place in strains which are genetically pure, and 

 that the purity is of relatively long standing. One can 

 only conclude that Davis's and Jeffrey's suggested cyto- 

 logical and morphological evidences of hybridity, if veri- 

 fied, will merely substitute hybridization for premutation 

 as a cause of germinal instability. They will not in any 

 way afford support to the Mendelian conception of 

 mutation. 



Nothing could be more obvious than the paths which 

 are marked out for the student of the CEnothera problem 

 by the interesting cytological clue afforded by the un- 

 paired chromosomes of CEnothera Lamarckiana and other 



