528 



Journal of Agricultural Research 



Vol. XIX, No. II 



Sterility might cause the elimination of certain gametic or zygotic 

 combinations, thus actually eliminating the sort desired. Zygotic com- 

 binations are sometimes eliminated as is the case with the homozygous 

 yellow mouse combination (7, 17) and with lethal factors in Drosophila 

 (jp). In some cases gametic combinations are eliminated. Such elimi- 

 nations occur as a result of pollen or ovule abortion. 



POLLEN ABORTION 



The presence of shriveled or abortive pollen grains is one means of 

 recognizing sterility. The method here used was to shake out pollen 

 from the heads upon a clean glass slide and then place a minute drop of 

 fuchsin on the pollen, then a drop of lactic acid, and a cover glass. ^ 

 By this method pollen was preserved for several weeks and could be 

 studied when it was convenient. 



The parent plants and F^ crosses were grown in 6-inch pots in the green- 

 house. A small percentage of small, globular, clear pollen grains were 

 observed. These, together with the occasional shriveled grains, were 

 counted as sterile. The results of these counts are given in Table I. 



Table I. — Counts of sterile pollen grains in wheat species and F, crosses between them 



Variety. 



Good 

 pollen. 



Poor 

 pollen. 



Parental species: 



Triticum vulgare 



TriticuTTi durum < 



Triticum durum 



Triticum dicoccum 



Fj crosses: 



Marquis X emmer (Minn. 1165). 



Emmer (Minn. 1165) X Marquis. 



Kubanka (C I 2094) X Marquis. . 



Marquis X Kubanka (C I 2094). . 



Marquis X Mindum 



Marquis 



Mindum 



Kubanka (C I 2094) . 

 Emmer (Minn. 1165). 



513 

 135 

 122 

 169 



475 

 340 

 113 



151 



lOI 



3 

 o 



19 



37 



9 



20 



12 



These results show that there is a larger percentage of shriveled and 

 abortive grains in the crosses than in the parental varieties. There is also 

 an indication of more pollen abortion in the durum-Marquis crosses than 

 in the cross between emmer and Marquis. 



COMPARISON OF NUMBER OF SEEDS SET IN Fj GENERATION AND PARENTS 



As a further test of sterility, counts were made of the number of barren 

 florets in several F^ crosses and their parents. 



There are two or more flowers in each wheat spikelet, and usually two 

 or three kernels mature. The outer florets of each spikelet are usually 

 most vigorous, and when only two florets per spikelet produce kernels 

 these are. usually the outside ones. Therefore, the two outer florets of 



1 Outlined to the writers by Dr. C. O. Rosendahl, Professor of Botany, University of Minnesota. 



