988 
Journal of Agricultural Research 
Vol. XXIV, No la 
but, rather, the method of classification shows the accuracy with which 
the determination of pure-line material could be made. 
Table IV .—The reaction of Kubanka No. 8 "KPentad and families to biologic Form 
XXXIV 
Parent varieties 
and P3 families. 
Class of infection. 
Distribution of Fs plants according to the type of 
infection shown. 
o 
2 X- 
X+ 4 
Total of 
pots of 
parent 
varie¬ 
ties 
or Ff 
fami¬ 
lies. 
Kubanka No. 8 
Do. 
Do.. 
Heterozygous. .. 
Near-susceptible 
Susceptible. 
IS 
6 
6 
14 
24 
14 
15 
136 
S 
S 
2S 
Total 
Pentad .... 
Do. 
Do. 
21 
71 
7 
44 
i6S 
3 S 
Resistant. 
Near-resistant 
Heterozygous. 
270 
36 
12 
30 
4 
2 
4 
7 
30 
4 
2 
Total 
Fs 
Do, 
Do, 
Do, 
Do, 
4 
318 
36 
II . 36 
Resistant. 
Near-resistant... 
Heterozygous. .. 
Near-susceptible 
Susceptible. 
70 
S2 
297 
S 
10 
183 
30 
108 
3 
13 
91 
31 
114 
256 
112 
1,025 
9 
S 
84 
20 
128 
Total 
425 
331 
16 
236 
i »393 
246 
The legitimacy of the foregoing method of analysis will become evident 
if a brief study is made of the type of data obtained and the object of the 
work. To make possible a classification which would form an adequate 
basis for the comparison of the reactions of the Fg hybrids with those of 
the parental varieties it was necessary to establish a range for the types 
of iiifection normal for each parent. It might appear that the total dis¬ 
tribution of types of infection of a parental variety should be considered 
its normal range, and the hybrid reactions judged accordingly. This 
would throw all the pots of each parent into a single class, viz, with 
Kubanka No. 8 there would be 35 pots in the susceptible class, which 
would be the same as ignoring the possibility of any error in the results. 
Obviously that would lead to inaccuracies in classifying the hybrids, for 
it is well established that even with carefully controlled conditions a 
certain amount of error is unavoidable. The method used has on the 
contrary much in its favor, for it tends to throw all doubtful F3 families 
into the near-susceptible, heterozygous, or near-resistant classes. 
Thirty-six control pots of Pentad were inoculated. Of the 369 plants 
that were infected, all but ii ranged from o to x— in type of infection. 
These ii showed infection of the x-f type. Classification of the pots on 
the same basis as was used in the case of Kubanka No. 8 resulted in 30 
being placed as resistant, 4 near-resistant, and 2 heterozygous (PI. I, A). 
The use of these terms to designate the different classes of infection is 
relative. It is convenient to call one parent susceptible and the other 
resistant regardless of whether the susceptibility or resistance is partial 
or complete. For the purpose of studying the genetics of the inheritance 
