FACTORS FOB YIELD AND QUALITY OF SPRING WHEAT 9 
Of the 152 dwarf F 2 plants grown at Bozeman in 1923, 114, or 75 
per cent, matured seed and 38, or 25 per cent, did not head and 
produce seed and were classed as grass clumps. Of the first class 
25 were grown at Bozeman in 1924. The breeding behavior of these 
strains in the F 3 generation is shown in Table 5. 
Of the 25 F 2 dwarf strains 4, or 16 per cent, bred true for dwarfness, 
and the remainder segregated in a ratio not significantly different 
from 3 dwarfs to 1 normal. Assuming that 16 per cent of the 114 
dwarfs in the F 2 population would have proved homozygous if 
tested, it appears that there were about 18 fertile homozygotes to 
be added to the 38 sterile grass clumps, making 56 in all. Correct- 
ing the F, Bozeman results on a percentage basis of F 3 plants grown 
at that station, the figures shown in Table 6 are obtained. 
Table 6. — Correction of the Bozeman F 2 dwarf data on the basis of F$ results 
Descriptive items 
>*•* ,£S5. 
Obtained (uncorrected) in F2 114 
■Corrected on basis of F3 96 
Calculated on 2 : 1 ratio 101 
Deviation 5 
Probable error 3.92 
This corrected deviation of 5 ±3.92 is a close fit to the expected 
2 : 1 ratio, as it is within three times the probable error. It is im- 
portant to note that at Bozeman in 1924 the four true-breeding F 2 
dwarf families all headed and matured seed. From these data it 
seems that the grass clumps appear only as a homozygous condition 
of dwarfness, the ability 01 the plants to head and mature seed being 
due to environmental conditions. 
An interpretation of the above data can be satisfactorily made on 
a genetic basis by assuming DD a factor for dwarfs and NN an in- 
hibitor or factor for normals. As Waldron (20) has shown, KotaX 
Marquis hybrids produce dwarfs in ratios involving two or three 
genetic factors, and Clark (5) observed no dwarfs in KotaX Hard 
Federation crosses, the formula for Marquis could be DDNN and 
Hard Federation ddnn, or vice versa. A dominant third factor 
necessary for dwarfness may be present in Marquis and Hard Fed- 
eration but lacking in Kola. As this would be common to the 
varieties dealt with here, it need not be represented in the formulas. 
The Fi of the Marquis X Hard Federation cross will thus be repre- 
sented as DdNn. The following formulas may represent the F 2 
genotypes and their breeding behavior in the F 3 generation: 
1 DDNN 
2 DdNN 
1 ddNN 
1 ddnn [Normals, breeding true to norm; 
4 DdNn Normals breeding 13 normals to 3 dwarfs. 
2 DDNn Normals, breeding 3 normals to 1 dwarf. 
2 Ddnn Dwarfs, breeding 3 dwarfs to 1 normal. 
1 DDnn Dwarfs, breeding true to dwarfs. 
79182—261 2 
