Feb. io, 1923 
Genetics of Bunt Resistance in Wheat 
453 
roots of the grape and produces galls or “ tuberosites” which, on the 
susceptible varieties, enlarge enormously, and in two or three years kill 
the vines. This growth is caused by a poison which is injected by the 
insect. The resistant varieties do not react to this poison, and in 
addition the insect does not multiply so rapidly on it, which indicates a 
repellant effect of the juice of the resistant plant on the life of the Phyl¬ 
loxera. Between two and three million acres of vineyards in France 
and California have been destroyed by Phylloxera during the past 
50 years and have been replanted to choice varieties that have been 
grafted on to resistant stocks. 
Little work has been done on the inheritance of disease resistance 
in animals. The nearest approach to an exhaustive critical investiga¬ 
tion in this subject, is that by Little and Tyzzer ( 26 ). They could trans¬ 
plant the carcinoma tumor designated as J. w. A. at will on the Japa¬ 
nese waltzing mouse, but the common mouse was immune to it. The F 1 
generation of these two races was very susceptible, there being but 1 
in 62 that failed to react. The F 2 and F s generations were very nearly 
immune, there being but 3 reacting positively out of 221. The Fj 
generation, back-crossed with the susceptible parent gave mostly sus¬ 
ceptible offspring (64 positive to 4 negative), but when back-crossed 
with the immune parent only immune offspring were produced (112 
negative reactions). Altogether 629 mice were used in the investiga¬ 
tion. The authors interpreted susceptibility to transplanted carcinoma 
tumor J. w. A. as being due to a complex of dominant multiple factors 
but considered their data insufficient to arrive at an approximation of 
the number involved. 
From the illustrations given above it will be seen that the researches 
already made on the inheritance of disease resistance indicate that, in 
the main, whether due to physical or chemical causes, Mendelian laws 
of segregation and recombination control resistance phenomena generally. 
Artificial crossing and selection of large numbers should help clear up 
the difficulties in making practical use of these laws in controlling crop 
and animal pests. 
BUNT RESISTANCE PHENOMENA IN WHEAT 
THE PARASITE 
There are two species of bunt, Tilletia tritici (Bjerk.) Wint. and T. levis 
Kuhn. T. tritici is the most common and is the one generally referred 
to in the literature, and, unless otherwise designated, is the species 
referred to throughout this paper. 
The smuts (order Ustilaginales) were among the first recognized 
plagues of plants. Pliny (41) and Theophrastus (54) wrote about 
smut outbreaks in grains and considered them due to untoward weather 
and soil conditions which caused a morbid transformation, that is, 
putrifaction, of the tissues of the grain. In 1801 Persoon (40, p. 224) 
described stinking-smut as being due to a fungus. Meyen (jj, p. 108- 
119) as late as 1841 wrote that the smut powder in a dissolved condi¬ 
tion entered the roots and caused the sap to engender the same disease. 
But Kuhn (2 j) was the first to prove that the fungus from the germinat¬ 
ing spore actually enters the young wheat plant, thereby starting infec¬ 
tion that results in the smutted head. 
