530 Journal of Agricultural Research voi. xix, No. n 



percentages of barren florets were 47.2 and 46.5, respectively. There 

 was about the same percentage of barrenness in emmer X Marquis, 

 emmer X Preston, and reciprocals — namely, 25.8 when emmer was the 

 female parent and 29 when emmer was the male parent. Thus, there is 

 apparently more sterility in the durum-Marquis cross than in the cross 

 between emmer and Marquis. 



Although no cytological examination was made to determine the time 

 of degeneration, it seems very likely that there is ovule as well as pollen 

 abortion. Barren florets, however, might be due to incompatibility of 

 certain genetic combinations or to slow growth of the pollen tube which 

 has been shown to occur in some species crosses (<?, 9). 



NATURAL CROSSES AS A POSSIBLE INDICATION OF STERILITY 



In 19 1 7 the Fj generation of durum X Marquis and durum X Haynes 

 Bluestem, as well as the parent sorts, were grown together. Marquis is an 

 awnless, glabrous chaffed wheat, Bluestem is an awnless wheat and has 

 pubescent chaff, while the durum varieties used have glabrous chaff and 

 are bearded. In the Fj generation of the durum-Marquis cross there 

 were a few individual plants with hairy chaff. Since these may have 

 been the result of natural hybridization, these plants were eliminated 

 from further consideration. 



In the F3 families of the durum-Marquis cross, each of which came from 

 an individual Fj plant, there were some hairy-chaffed plants. In some 

 families the number of plants with hairy chaff was rather large, and 

 counts were made to determine the frequency of their occurrence. Fully 

 bearded plants have always been found to breed true for this character 

 (14) . This fact supports the view that natural crossing may be the cause 

 of the hairy plants found in several of the F3 families. 



The most convincing evidence of natural crossing comes from the F3 

 generation grown from glabrous-chaffed, bearded F2 plants of crosses 

 between lumillo or Kubanka with Marquis. Table III records the 

 number of plants produced in different families as well as the number 

 of bearded smooth, hairy, intermediate-awned, and intermediate-awned 

 glabrous-chaffed plants. It is significant that all plants with hairy chaff 

 had intermediate awns. This would be expected in the Fj generation of 

 a cross between bearded wheats and so-called awnless varieties such as 

 Marquis or Bluestem. It is apparent that the amount of natural crossing 

 varies in different families. For example, 196-26 produced 7 bearded, 

 glabrous-chaffed plants and 7 intermediate-awned, hairy-chaft'ed plants, 

 while family 214-35 produced 60 bearded plants. 



The progeny of a few selected glabrous-chaffed, intermediate-awned 

 Fj plants of the cross between Marquis and durum are classified in Table 

 IV. The parent Fj sorts were classified as glabrous-chaffed, intermediate- 

 awned. All such plants produced both bearded, awnless, and inter- 

 mediate-awned plants in the F3 generation. Numerous hairy-chaffed 



