Jime 23,1923 
Inheritance of Resistance to Puccinia graminis 
985 
Amautka seed was known to be impure. This explains why 8 out of the 
28 plants inoculated did not appear to be immune. Hayes {14) and 
Hayes and Garber (15, p. 35~36y 77-7^) have reported from 2 to 3 per 
cent of natural crossing in wheat grown at St. Paul, Minn. A rather large 
difference is shown between the inoculations of February 10 and February 
20 on Pentad. This demonstrates the value of running several pots* of 
the parental varieties with each set of hybrid families. 
From the foregoing discussion it should not be concluded that the 
variations were so great as to obscure the results. The reaction of the 
Fg plants to the different forms of rust was constant within certain 
limits and the fact that the plants which were tested were of the third 
hybrid generation, and consisted of families each arising from a single 
Fg plant, makes the interpretation of the various reactions a fairly 
definite matter. 
BASIS FOR INTERPRI^TING RESULTS 
As the determination of the genetic nature of resistance was the chief 
object of this investigation, the results obtained were interpreted on 
the basis of the reactions of the parental varieties to the forms of rust 
used. The Fg families were placed in five classes with reference to 
reaction to the different biologic forms, viz, resistant, near-resistant, 
heterozygous, near-susceptible, and susceptible. In the work with 
Form I the class designations “immune” and “near-immune” were 
used instead of “resistant” and “near-resistant” owing to the nature 
of the Mindum reaction. 
Fg families showing resistance similar to that of the resistant parent 
were termed resistant. Similarly, the Fg families showing susceptibility 
equivalent to that of the susceptible parent were classed as susceptible. 
Those Fg families having 9 or more apparently resistant plants and one 
plant showing susceptibility were classed as near-resistant. Likewise 
Fg families with 9 or more plants showing susceptibility and one plant 
appearing resistant were placed as near-susceptible. 
It is probable that some of the Fg families placed in the near-resistant 
or near-susceptible class were in reality heterozygous. It is also probable 
that others placed in these classes were resistant or susceptible, respec¬ 
tively. Owing to the likelihood of the occurrence of certain errors, 
which have been discussed in a previous section of this paper, it was not 
possible to determine the exact genetic nature of the “near-resistant” 
and “near-susceptible” Fg families. It was best, therefore, to leave 
these doubtful Fg families in classes which by their names indicate 
their character. 
All Fg families not falling in one of the preceding four classes were 
termed hetercwygous. The heterozygosity of various Fg families varied 
from a preponderance of apparently susceptible plants to a preponder¬ 
ance of plants showing resistance. Of the five different classes the 
resistant class is of greatest importance, as it represents the Fg families 
which appeared homozygous for resistance. 
8 The word “pot" is used throughout this article to denote the group of plants of a pure line parent 
variety growing in a single pot, such a group being comparable to a group of F3 plants (an F3 family) 
likewise growing in one pot- 
