46 



The Journal of Heredity 



peared because of a natural cross be- 

 tween a dark fatua and Garton 784. 



In comparing the size and shape of 

 seed of the three different phenotypes 

 growing in rows segregating for false 

 wild oats with the seed phenotypes of 

 the F2 generations of artificial fatua- 

 sativa and fatua-orientalis crosses, 

 (Figures 23 and 24) considerable dif- 

 ferences are apparent. False wild 

 Aurora seed is very similar in size and 

 shape to the seed of true Aurora; a 

 similar relation holds between the false 

 wild and cultivated forms of Garton 

 784 and Victory respectively. In the 

 F2 generations of actual crosses between 

 fatua and cultivated varieties it is 

 clear that segregation occurred. Here 

 again if one accepts natural crossing 

 as the explanation of the origin of false 

 wild oats, one must postulate that an 

 elimination of phenotypes with respect 

 to size and shape of seed has taken 

 place or that the progeny of a natural 

 cross between fatua and cultivated 

 forms did not show segregation with 

 respect to these seed characters. 



Either of the two explanations is 

 quite unlikely, particularly in the case 

 of false wild Aurora. It is more prob- 

 able that Nilsson-Ehle's hypothesis is 

 correct, namely that the origin of false 

 wild oats is the result of a mutation. 

 The exclusive occurrence of monohy- 

 brid segregation among the progeny 

 of heterozygous false wild oats is in 

 itself evidence of a mutation. The 

 single factor difference between the 

 false wild oat and the respective variety 

 in which it was found can most easily 

 be explained as a mutation i.e., a 

 change in the chromosomal locus which 

 is concerned with the phenotypic ex- 

 pression of awn development, seed 

 articulation, and pubescence around 

 the articulation. It is true that mono- 

 hybrid segregation also occurs with 

 respect to character of seed articulation 

 and certain closely associated charac- 

 ters in fatua-sativa and fatua-orientalis 

 crosses but in addition there is segrega- 

 tion for characters not closely asso- 

 ciated with the type of articulation. 



This is important evidence in connec- 

 tion with considering the origin of false 

 wild oats. 



Nilsson-Ehle points out one objec- 

 tion to Zade's hypothesis in explaining 

 the origin of the false wild oats ob- 

 served by the former. Fatua oats are 

 not found in the vicinity of Svalof. 

 Zade found a positive correlation 

 between the number of fatua forms 

 and the number of "intermediate" 

 (heterozygous false wild oats) forms 

 present in any particular variety. 

 Tschermak and Zade also suggest that 

 natural crosses between cultivated 

 varieties may explain the origin of false 

 wild oats. This explanation is open 

 to objections similar to the ones 

 pointed out against accepting the 

 hypothesis that false wild oats are due 

 to natural crosses between fatua and 

 cultivated oats. A satisfactory ex- 

 planation other than a mutation for the 

 exclusive occurrence of monohybrid 

 segregation in the progeny of hetero- 

 gygous false wild individuals has not 

 been made. In the twelve pure lines, 

 two commercial varieties and one F2 

 generation of a cross (Glockenhafer 

 II X Grossmogul) in which Nilsson- 

 Ehle found false wild oats and in the 

 three varieties of very different mor- 

 phological aspect reported in this paper, 

 the false wild oats and the respective 

 variety in which they appeared differ 

 only in awn development, articulation 

 of the seed, and pubescence around the 

 articulation. These three characters 

 are conditioned by a single factor 

 difference. Moreover, if natural cross- 

 ing between cultivated forms is the 

 cause of false wild oats it is rather sin- 

 gular that apparently they have not 

 been observed or at least not reported 

 more frequently by plant breeders who 

 have made extensive studies in oat 

 hybridization. 



The false wild oats in Victory were 

 discovered in the second generation of 

 the progeny of a single plant selection. 

 From^ the time the plant selection was 

 made until the false wild oats were 

 discovered this particular strain was 



* Information furnished by^the~courtesy of the Plant Breeding Section of the University 

 of Minnesota. ~ 



