992 
Journal of Agricultural Research 
Vol. XXIV, No 13 
very little chlorosis and no necrosis. Here, however, about 50 per cent 
of the type 4 uredinia showed such a decided necrotic bordering that the 
advisability of creating a special class for this type of infection was con¬ 
sidered. Eventually it was concluded that the establishment of an ad¬ 
ditional type would possibly lead to some confusion without really prov¬ 
ing of value, as it was apparent that plants infected in this manner were 
susceptible, on account of the development of numerous large uredinia. 
A total of no Fj families were tested. There were 1,711 Fg plants in¬ 
oculated, of which 1,604 showed infection. The distribution of Fg plants 
is summarized in Table VI. Classification of the no Fg families gave 14 
as resistant, 6 near-resistant, 68 heterozygous, n near-susceptible, and 
n susceptible (PI. 3). Since between a third and a fourth of the Pentad 
pots were placed outside of the resistant class, it may be considered that 
14 plus 4 or 18 Fg families were as resistant as the resistant parent. This 
number of resistant families is too small to indicate definitely the pres¬ 
ence of a single factor, and it is much too large to make a two-factor 
hypothesis feasible. The single factor is the more plausible explanation. 
If the near-resistant and resistant classes are grouped together, and 
similarly, the near-susceptible and susceptible classes, a fairly satisfac¬ 
tory 1:2 :i ratio is obtained. The presence of a single factor would ap¬ 
pear probable in this case. The results do not make possible a more 
exact genetic analysis. Examination of the distribution of Fg plants in 
the heterozygous class showed a lack of dominance for either suscepti¬ 
bility or resistance. 
COMBINATIONS OF SUSCFPTIBIUTY AND RFSlSTANClS OF MINDUM X PFNTAD 
Fg FAMILIES TO FORM I AND FORM XXXIV 
Table VII correlates the results obtained with Form I and Form 
XXXIV for those families which were inoculated with both forms. Vari¬ 
ous combinations of susceptibility, resistance, and heterozygosity to the 
two biologic forms appear. Six Fg families were definitely resistant to 
Form XXXIV and immune from Form I as, for example, 809-21, 805-16, 
and 796-4 (PI. 4, A, B, C). Two families were quite susceptible to both 
forms, as 804-7 (PI. 4, E). Other families were resistant to or immune 
from one form and susceptible to the other. Still other Fg families were 
resistant or susceptible to one form and heterozygous to the other, as 
806-24 (PI. 4, D). Many families were heterozygous to both forms. 
There were also combinations of near-resistance and near-susceptibility, 
as 809-8 (PI. 4, F). 
TabIvF VII .—The classified reaction of MindumXPentad families to biologic Forms I 
and XXXIV 
Reaction to Form XXXIV'. 
Reaction to Form I. 
Total. 
Immime. 
Near- 
immune. 
Heterozy¬ 
gous. 
Near- 
susceptible. 
Suscepti¬ 
ble. 
Resistant. 
6 
0 
8 
0 
0 
14 
Near-resistant. 
I 
0 
2 
I 
I 
5 
Heterozygous. 
14 
7 
36 
3 
7 
67 
Near-susceptible. 
3 
I 
5 
I 
I 
II 
Susceptible. 
3 
I 
3 
I 
2 
10 
Total. 
27 
9 
54 
6 
II 
107 
