304 



The Journal of Heredity 



that possibly existing in the prohfic 

 dwarf previously described, provided 

 the tall plants appearing in the progeny 

 of the one plant were the result of a 

 recombination of certain factors instead 

 of accidental admixtures. These data 

 indicate that the dwarf character is 

 dominant, and the tall character reces- 

 sive. This condition, therefore, is 

 directly the reverse to that shown by 

 Warburton in the dwarf plants from 

 Victory. 



The three mother-dwarf plants pro- 

 duced in 1 92 1 as well as the seventy- 

 five grown in 1922 wers decidedly late 

 in maturity and not very prolific. The 

 l)rogeny of one of the dwarf plants is 

 shown in Figure 5. In most characters 

 they resemble very closely the dwarfs 

 described by Warburton. 



Discussion of Results 



Assuming that the two tall plants 

 appearing in the relatively large dwarf 

 progeny from the Aurora X Pringle 

 Progress cross were accidental mix- 

 tures, and that the dwarf character in 

 this cross behaves as a pure recessive, 

 there still remains some explanation 

 to be made of the directly reversed 

 behavior shown in the progeny of 

 the dwarf plants from the Winter 

 Turf X Sixty-Day cross. One ex- 

 planation for the appearance of the 

 apparently heterozygous dwarf is that 

 it arose as a result of a mutation af- 

 fecting either the pollen or egg cells 

 of a normal plant and resulting in the 

 genotypic make-up D'^ d'^, for the 

 dwarf, assuming that D denotes the 

 presence of the factor for dwarf ness. 

 In the next generation this would pro- 

 duce the following : 



■ D' D" Dwarfs 3 

 2 D^ d<^ ^ 



I d^ d<^ Normal i 



thus giving a simple Mendelian mono- 

 hybrid ratio of three dwarfs to one 

 tall, as indicated by the data in Table 



2. The origin of the heterozygous 

 dwarf possibly is not so simple as the 

 above explanation would indicate. 



In order to obtain additional data 

 on the behavior of this dwarf, indi- 

 vidual progenies of all plants pro- 

 ducing seed from the three segregating 

 rows will be grown in 1923. The seg- 

 regates homozygous for dwarfness will 

 thus be determined. These then will 

 be l)ack-crossed on the homozygous 

 tails in an attempt to determine the 

 various factors involved in the produc- 

 tion of the heterozygous dwarf. 



Miyazawa" very recently has report- 

 ed similar hereditary behavior of a 

 dwarf form of barley in which the 

 dwarf character is dominant and the 

 dwarf plants are heterozygous, a pure 

 dwarf condition apparently being lethal. 

 He obtained a ratio of approximately 

 two dwarfs to one normal, instead of 

 a ratio of three to one, from which 

 he concluded that typical segregation 

 was not shown. In further investiga- 

 tions with this dwarf he discovered 

 among his seedlings a new dwarf form 

 ( a sterile dwarf ) which tillered freely, 

 but grew very slowly and produced no 

 seed, the length of the culm being 

 markedly shorter than that of the orig- 

 inal or non-sterile dwarf. Of 684 

 plants grown he classed 156 as sterile 

 dwarfs, 340 as non-sterile dwarfs, and 

 188 as normal, the ratio of the three 

 types thus being approximately 1:2:1. 

 The original dwarf found in 191 5 was 

 described as being intermediate exter- 

 nally, that is, shorter than normal, but 

 taller than the sterile dwarf. Theor- 

 etically he concludes that if the allelo- 

 morph for dwarfness and absence of 

 dwarfness is denoted by D and d, re- 

 spectively, the sterile dwarf = DD, 

 the normal ^dd, and the ordinary 

 dwarf =^ Dd. On the basis of this 

 ex]jlanation he suggests that the seed 

 which first produced the dwarf plant, 

 Dd, may have arisen from dd by mu- 

 tation. 



"MiYAzAWA, Br.\(;o. Hereditary Behavior of a Dwarf Form of Barlej' in Japan: 

 Jourl. Genetics, xi:205-2o8; i plate, Cambridge, Dec. 1921. 



