302 



The Journal of Heredity 



the dwarfs appeared in 1921. Of the 

 remaining ten, five were discarded and 

 further selections were made from the 

 others. These third generation progen- 

 ies, including the nine bulked strains 

 and the reselections, again were grown 

 in five-foot rows at Aberdeen in 1919. 

 In 1920 the strain 1019 ai-i2B, along 

 with twenty-four others of this cross, 

 were advanced to the rod-row nursery 

 at Aberdeen. At harvest time these 

 rows were cut in the usual manner, 

 but no dwarfs were noted in the row 

 of 1019 ai-i2B. In 1921 these same 

 strains were once more included in 

 the rod-row nursery at Aberdeen, and 

 at harvest the eight dwarf plants were 

 observed in the row of selection 1019 

 ai-i2B, the dwarfs thus appearing in 

 the sixth hybrid generation of the 

 cross. 



Progeny of the Dwarf Plants 



The eight dwarf plants were harvest- 

 ed individually and sown in five-foot 

 rows at Aberdeen in the spring of 



1922. The eight plants bred true for 

 dwarfness, with the exception of one 

 row, in which two tall plants appeared. 

 It is possible that these two plants were 

 accidental mixtures and not plant segre- 

 gates. One was yellow-seeded like the 

 Aurora parent, and the second was 

 black-seeded unlike the other parent, 

 Pringle Progress, which is a white oat. 

 To determine the genotypic make-up 

 of the two tall plants, individual pro- 

 genies from them will be grown in 



1923, as well as from the dwarfs in 

 this row. The eight dwarf mother 

 plants produced about 230 dwarf 

 plants. 



One of the most interesting things 

 about this dwarf is its prolificacy. Prac- 

 tically every culm produced a small 

 panicle with numerous spikelets. The 

 plants were distinctly turf-like, in 

 which character they were similar to 

 the dwarfs from Victory oats, de- 

 scribed by Warburton.^ However, in 

 earliness and prolificacy it is distinct 



from the Victory dwarf. This new 

 dwarf is quite early and produces fully 

 ripened grain in abundance, while the 

 Victory dwarf is very late and barely 

 ripens sufficient seed to reproduce it- 

 self. The prolificacy of the dwarf 

 plants grown at Aberdeen in 1922 is 

 shown in Figure 4. 



The genotypic composition of the 

 dwarf form has not been determined 

 by crossing it with the normal tall, 

 but it is possible that it will behave 

 as a pure recessive, as was the case 

 in the dwarf reported by Warburton. 

 The fact that it was not found until 

 the sixth hybrid generation may be due 

 to its having been masked in some 

 unknown manner, becoming apparent 

 only after proper recombination of 

 factors had occurred. On the other 

 hand, if the two tall plants appearing 

 in the progeny of the one dwarf plant 

 are the result of segregation a_ condi- 

 tion directly the reverse of that shown 

 by Warburton is evident, that is, the 

 tall character must be considered as 

 recessive and the dwarf character as 

 dominant. It also is possible that the 

 dwarfs may be mutations, or that they 

 may be due to some combination that 

 is not simple in nature. That the con- 

 dition is complex is evidenced by the 

 dwarfs not appearing in generations 

 earlier than the sixth. 



Dwarfness in Other Hybrids 



In 1 92 1, dwarf oats also appeared 

 at Aberdeen in the progeny of another 

 cross. The plant material in which 

 this dwarf appeared represented the 

 fourth generation progeny of a cross 

 between Winter Turf and Sixty-Day. 

 In all, eight progenies of this cross 

 were grown in plant rows at Aberdeen 

 in 1921, which represented plant selec- 

 tions from third generation material. 

 Of these eight progenies, three pro- 

 duced one dwarf plant each. The num- 

 ber of dwarf and tall plants produced 

 in the three segregating rows in 192? 

 is shown in Table i. 



^ Warburton, C. W. The Occurrence of Dwarfness in Oats. Jourl. Amer. Soc. Agron., 

 xi :72-76. 1919. 



