474 
Journal of Agricultural Research voi. xxiii, No. 6 
host, more than 80 per cent of the plants on the average produce only the 
fruiting bodies of the parasite, and the others produce less than 40 per 
cent of grain. Fortyfold and Red Russian, which are intermediate in 
respect to total bunt produced, are also intermediate in respect to the 
amount of wheat produced on the infected heads. 
The resistance of Turkey is different from that of Alaska, for segregates 
of a cross betwen them occurred which were more resistant than either 
parent, inasmuch as no trace of bunt could be obtained from the F 3 to 
the F 7 generation, although planted under conditions favoring maximum 
infection—conditions under which both parents showed traces of bunt 
on more than one-fourth of the plants. Such a result would be impossible 
unless the resistance of the two wheats were cumulative in effect, each 
contributing something that the other lacked. For if the resistance were 
the same in both parents, the offspring would fluctuate around the same 
mean and no segregates would occur more resistant or more susceptible 
than the parents. If, however, the resistance of Turkey and Alaska were 
due to different causes, or perhaps the genes located in different chromo¬ 
somes, then the offspring would show greater variation than the parents* 
and segregates would occur which would be permanently more suscep¬ 
tible than either as well as more resistant. If the resistance of each 
parent were composed of differing multiple factors, many new and differ¬ 
ent segregates would occur. Thus, if Turkey resistance abc met Alaska 
resistance xyz, and each factor reduced the amount of bunt by 20 per 
cent, a cross between them should give varients (assuming the suscep¬ 
tibility of the parents separately to be 5 per cent) in the F 2 generation 
that would produce bunt as follows: 
Number of 
resistant fac¬ 
tors. 
Bunt pro¬ 
duced. 
Classification. 
Number of 
resistant fac¬ 
tors. 
Blunt pro¬ 
duced. 
Classification. 
0 .. . . 
Per cent. 
65 
45 
25 
Nonresistant. 
Slightly resistant. 
Somewhat resist¬ 
ant. 
•2 . 
Per cent. 
5 
-15 0 
~35 0 
-55 0 
Very resistant. 
Immune. 
Do. 
Do. 
I . 
O . 
4 , . .. 
2 . 
c . 
6. 
Unfortunately the large number of sterile plants and flowers produced 
by crossing Turkey and Alaska, combined with the lack of winter hardi¬ 
ness, reduced the number of plants to such a degree that an accurate 
analysis of the particular type of segregation that occurred was 
impossible. 
Florence is a very resistant spring wheat, but its resistance is also 
different from that of Turkey, for transgressive inheritance occurred in a 
cross between them, F 3 segregates occurring all the way from completely 
immune to completely susceptible individuals, not unlike the illustration 
given above. More than 40 per cent were immune, while the plants in 
12 rows (7 per cent of the F 3 progeny) were more than 50 per cent bunt, an 
amount never produced by either parent under the most favorable con¬ 
ditions for infection. Something like 30 per cent of the rows were inter¬ 
mediate, producing from 10 to 50 per cent of bunted heads. 
It is not too much to suppose that the 72 immune rows differed in the 
intensity of their resistance, but there is no way of proving it except by 
the slow, laborious process of crossing them with susceptible varieties 
