Nos. 622-623] HYBRIDS IN EGYPTIAN COTTON 



503 



The Back-Crossed Hyi 



The means of the % back-crossed hybrids for nearly 

 all characters showed departures from the midpoint of 

 the parental means which were both significant and to- 

 wards the mean of the respective preponderant parent 

 (Pima or Gila). In the % back-crosses, the mean vir- 

 tually coincided with those of the preponderant parent, 

 as the following data show: 



The distributions, for leaf index and boll index, of the 

 Pima % back-cross, were embraced by those of Pima and 

 the distributions of the Gila % back-cross were embraced 

 by those of Gila. It is therefore apparent that twice 

 back-crossing the simple hybrid with either of its parents 

 has sufficed to eliminate the influence of the other parent 

 in the expression of these characters. 



Absence of Mutants 

 Careful examination, in 1916, of every plant in the F 2 

 progenies of the simple hybrids and in the % back-cross 

 progenies, showed only various recombinations of the 

 Pima and Gila characters. A large majority of the 

 simple hybrid plants were approximately intermediate, 

 although occasional individuals showed a near approach 

 to one or the other parent. Most of the back-cross 

 plants, as compared with the simple hybrid individuals, 

 showed clearly the preponderating influence of the % 

 parent, but few if any plants in the % back-cross pro- 

 genies could have been classed as wholly Pima or wholly 

 Gila, the influence of the one-quarter parent being ob- 

 servable in the great majority of cases. No instance of 



Pima I 

 Gila i ■ 



78.1 ± .14 



i-cross [(P X G) X P] X P 78.7 ± .63 

 c-eross [(P X G) X G] X G 94.1 ± .47 



173 ± .18 

 179 ± .66 



