360 Journal of Agricultural Research voi. xxii. no. 7 



If wheats segregate trom these crosses it will prove further the correct- 

 ness of the two-factor hypothesis. It will also lead to the expectation 

 that genotypic forms similar to the above, and other combinations as 

 well, exist among the so-called pure commercial spelt forms and when the 

 proper cross is made among these commercial spelts, a certain number 

 of synthetic wheats may be produced in the Fj generation. 



It is easy to understand how the wheat character, being distinctly 

 hypostatic, may be carried from generation to generation by the spelt 

 type. But how can the spelt type segregate from a wheat X wheat cross? 

 How can one conceive the spelt factor, which is so pronouncedly epistatic 

 to the wheat character, as being carried by a wheat without being mani- 

 fested phenotypically ? The explanation is simple. It was shown that 

 modifiers are involved in these crosses. Common wheats occasionally 

 carry modifiers which tend to dilute the spelt character. Some of these 

 modifiers were shown to be so effective that they grouped all of the spelts 

 in class 9. Most of the class 9 individuals, as recorded in the foregoing 

 tables, resemble wheat so closely that no one would be likely to call 

 them true spelts. 



If a certain diluting modifier can shift the spelts to class 9, a group of 

 these may readily shift the spelt to classes between 9 and 10. If these 

 diluting factors are reduced to a homozygous dominant condition, the 

 dilute spelt which will be classified as 10 will breed true to type and be 

 considered as wheat, although from a genetic standpoint such a form is 

 a spelt. 



As long as such sorts are allowed to self-fertilize they will produce a 

 so-called pure line consisting of a constant wheat type. Their spelt 

 characteristics are exhibited only when crossed with a common wheat 

 which carries the factor for dilution in a recessive state. In the second 

 generation of this cross the segregates which carry the S factor with the 

 factor for dilution in a recessive state; that is, SS dd, will be spelts. 



Fortunately, experimental evidence can be cited to support this 

 statement. One of the writers has observed at the Kansas Agricultural 

 Experiment Station over 20 spelts among Fj hybrid plants derived 

 from a number of wheat X wheat crosses where one of the parents was 

 a rust-resistant variety of winter wheat and the other was Preston, 

 Marquis, or Haynes Bluestem, well-known varieties of spring wheats. 

 These parental types and some of the spelt segregates are shown in 

 Plate 33, B.^ 



None of the F^ plants in these crosses were spelts, or at least passed for 

 spelts, although they might have shown some spelt characteristics in a 

 weak form. In the Fj generation, however, depending upon the cross, 

 the proportions of wheat to spelts varied roughly from 3 to i to over 



' The authors are indebted to Professors John H. Parker and L. E. Melchers for allowing them to photo- 

 graph these forms and use them in connection with this paper. 



