WHITE— STUDIES OF INHERITANCE IN PISUM. 



553 



Purple flower X white flower in F^ give all purple-flowered 

 progeny. In F,, generally only purple- and white-flowered segre- 

 gates in an approximation to the 3 : i ratio are obtained. Mendel's 

 results from a total of 929 Fj were: 



705 purple red: 224 whites or a ratio of 3-15: i. 



In F3 the whites tested and approximately one third of the 100 

 tested purple reds bred true, while about two thirds (64 F^ ind.) 

 gave purple reds and whites again. 



In crosses of certain true breeding white segregates with purple- 

 flowered races, purples are obtained in F^, while in F,, purples, 

 pinks and whites occur in proportions approximating 9:3:4. 



Pink-flowered varieties crossed with each other generally give 

 nothing but pinks in F^ and succeeding generations. 



Pink flower X white flower in F^ commonly gives all purple-red- 

 flowered offspring, which in Fg give purples, pinks and whites in a 

 ratio of 9:3:4. Lock (56) and Tschermak (86) obtained the fol- 

 lowing results : 



In F3, the F2 whites and part of the F, purples and pinks breed 

 true, but the greater proportion of the latter two classes break up 

 again, the purples giving either purples, pinks, whites ; purples and 

 whites, or purples and pinks, while the heterozygous pinks only 

 give pinks and whites in a ratio of 3:1, the actual results obtained 

 by Lock (56) being 113 pinks : 50 whites. Out of 16 F, pinks 6 

 bred true in F3 while 10 were heterozygous for pink and white. 



Back-crosses of the F^ of this cross with pure white-flowered 

 varieties gave 44 purple and 26 white-flowered plants, the theoret- 

 ically expected being 35 of each. Back-crosses of this same purple 

 F^ with the pure pink strain gave 21 purple and 17 pinks, where an 

 equal number of each was expected. Back-crosses of F2 purples 

 and whites with pure white and pure pink varieties gave results 

 showing there were two genetic sorts of whites. 



