STRAIN AND INDIVIDUAL IDIOSYNCRASIES. 



In numerous conversations with Luther Burbank the distinguished 

 plant-breeder of Santa Rosa, California, I have heard a certain phrase 

 fall often from his lips. Many years of close observation and of ex- 

 traordinarily wide experimentation in inheritance have deeply impressed 

 on Burbank the actuality of "individual idiosyncrasy" in the matters of 

 heredity. And I use this term as expressing what I believe actually to 

 exist in the case of the silkworms. Coupled with it I use also the 

 phrase "strain idiosyncrasy" to indicate a varying inheritance behavior 

 of certain characteristics according to races or strains of long breeding. 



These phrases are not used to obscure explanation or to relegate 

 the matter to hopeless confusion there is of course regularity at the 

 bottom somewhere but are used because no generalization or law of 

 inheritance so far formulated seems to offer an expression or explana- 

 tion sufficiently defining the actual phenomena or order of inheritance 

 as exhibited by the silkworms (and by other animals). 



As examples of the condition described as "individual idiosyn- 

 crasy," we may take the following: 



$ Bagdad pure race, white larva, white cocoon X J Italian Salmon, 

 pure race, tiger-banded larva, salmon cocoon; produced 135 tiger-band, 

 129 white larvae, and all salmon cocoons. 



$ Italian Salmon pure race, tiger-banded larva, salmon cocoon, X 

 5 Bagdad pure race, white larva, white cocoon ; produced all tiger-band 

 larvae, and all white cocoons. 



$ Bagdad pure race, white larva, white cocoon, X J Italian Salmon, 

 pure race, tiger-banded larva, salmon cocoon ; produced all tiger-band 

 larvae and 78 white cocoons and 71 salmon. 



Now the differences in the larval inheritance in these three first 

 cross rearings are explicable on the basis of the Italian Salmon parent 

 having been a homozygote (as regards the larval characteristic) in 

 two cases and a heterozygote in one. But the differences in cocoon 

 character inheritance are not to be so explained. 



In the F 2 generations from intermated hybrids of these rearings 

 the larvae in all cases (except white X white) segregated according to 

 parental characters and did so in Mendelian proportions; the cocoons 

 also segregated according to the parental characters and also did so in 

 most cases with some approximation to Mendelian proportions. 



Now to illustrate "strain idiosyncrasy." 



