PURE LINE INHERITANCE AXD PARTHENOGENESIS. 



H. E. EWING. 



INTRODUCTION. 



Ever since Johanssen, by his epoch-making researches with 

 self-fertilized strains of beans, established his pure line con- 

 ception of heredity, other investigators have been extending 

 this conception so as to have it include many forms which do 

 not reproduce sexually. In fact some of these investigators 

 hold that all selections made within isolated strains of asexually 

 reproducing plants and animals will fail to alter in the least the 

 fraternal mean of succeeding generations. 



Some careful work already has been done with lower organisms, 

 which shows that Johanssen's pure line conception holds true 

 for forms reproducing by fission or budding. Up to the present 

 time no extensive work has been done with parthenogenetic 

 animals. In fact the only paper which I have found dealing 

 with selections among parthenogenetic forms is one by Kelly. 

 Kelly worked with an aphid, Aphis nimicis, but did not carry 

 his selections beyond two generations. However, he came to 

 the conclusion that, "the progeny does not inherit the somatic 

 idiosyncrasies of the parent, but does inherit from the underlying 

 germ plasm common to all." 



During the winter of 1910-'! I, I began a series of experiments 

 along pure lines with the cabbage aphis, Aphis brassica Linn., 

 but while moving about from one part of the country to another 

 I confined the individuals too closely in their breeding cells with 

 the unfortunate result that they all died. 



Again during the summer of 1912 I took up similar experi- 

 ments with our common black cherry aphis, Myzits cerasi Fab., 

 but before I obtained a sufficient number of generations to make 

 the results reliable, cold weather set in causing the sexual forms 

 to appear, thus spoiling my result >. 



\Yhile working this last winter with the European grain aphis, 

 Aphis ai'oicc Fab., I noticed its great variations, and since the 



-S 



