Feb. 10, 1933 
Genetics of Bunt Resistance in Wheat 
447 
5. Hypersensitiveness of the host seems to be a common phenomenon not only 
among plants somewhat resistant to P. graminis but also among those almost totally 
immune to it. 
These conclusions point to the probability that resistant and sus¬ 
ceptible plants differ in the chemical composition of their cell walls or 
protoplasm or both. Valuable information might be gained along these 
lines by such investigations as the recent work of Rumbold (43) and 
Thiel and Weiss (55). Rumbold killed Chestnut trees by injecting an 
extract of the cankerous tissue caused by the chestnut-blight fungus 
[Endothia parasitica (Murr.) P. J. and H. W. Anderson] into the trunks of 
healthy trees. Extracts from healthy tissue produced no effect. 
Thiel and Weiss were able to germinate teliospores of Puccinia graminis 
tritici Erikss. and Henn. in midwinter by soaking them 15 minutes in 1 
per cent citric acid, although untreated spores would not germinate at 
all until spring. Other acids, lipoid solvents, and sodium hydroxid were 
ineffective. From this it would seem that the acid had acted as a 
specific activator through the cell wall on the protoplasm. Susceptible 
hosts may contain similar activators which stimulate the metabolism 
of the parasite. 
The delicate chemotactic balance between host and parasite as an ex¬ 
planation of the differing degrees of resistance finds support in the in¬ 
vestigations of Spinks (44) who found that nitrates, and especially lead 
and zinc nitrate, increased the susceptibility of wheat and barley to 
mildew and rust. Furthermore, potash and lithium salts decreased sus¬ 
ceptibility; but resistant varieties maintained their relative resistance 
under either condition. 
From this it is logical to assume that species or races which vary in 
their resistance to disease-causing organisms when growing under iden¬ 
tical environmental conditions do so because of their physical and 
chemical individualism. If this be true, then the complex of causes 
responsible for resistance and immunity in plants is very similar to, if 
not identical with, those producing resistance and immunity in animals. 
The classic researches the last 25 years in the antitoxin laboratories 
have shown that susceptibility to disease is caused by the physico¬ 
chemical reactions of poisons, toxins, ptomains, etc., produced by the 
causal organism in the various tissues of the host. In acquired immunity 
the host cells have the power to develop counteracting chemicals which 
neutralize the harmful substances produced by the pathogene. In 
natural immunity either the counteracting chemicals are already pre¬ 
sent, the temperature, light, food, etc., are not optimum for the patho¬ 
gene, or else the composition of the protoplasm of the host is such that 
no chemical reaction takes place. An illustration of the latter condition 
is described by Zinsser (62) regarding tetanus from the work of Blu- 
menthal (6, p. 183). As is well known, the central nervous system is 
the special point of attack for tetanus poison, and Blumenthal found that 
tetanus toxin was neutralized by the brain tissue of susceptible animals, 
but the brain tissue of resistant animals like the chicken had little or 
no neutralizing power. The frog is also immune to tetanus under normal 
conditions. When the toxin is injected, the body temperature being too 
low to allow the combination between toxin and nervous tissue to take 
place, no tetanus results. If, however, the frog is placed in a tank of 
warm water and kept at the normal temperature of the human body it 
succumbs to the effects of the toxin. Clearly chickens and frogs are 
