450 
Journal of Agricultural Research 
Vol. XXIII, No. 6 
parasite, there is a physico-chemcial complex so intricate that it has 
thus far been impossible to comprehend or to analyze it in all its detail. 
Heritable resistance represents a permanent upsetting of this balance in 
favor of the host, caused by the variation in its physico-chemical complex. 
inheritance oe resistance 
Acquired resistance and induced immunity, like other acquired 
characters, have not been shown experimentally to be inherited in the 
ordinary sense of the term, but each generation must recover from a 
given disease or be vaccinated (or inoculated with the proper virus) in 
order to acquire immunity. Inherent or natural resistance is definitely 
passed on from generation to generation like morphological characters. 
When such a resistant race is crossed on a susceptible one, resistant and 
susceptible races may be isolated in subsequent generations, which show 
that the same laws of inheritance which control other characteristics are 
in operation in determining the causes of resistance. Biffn (2), in Eng¬ 
land, found resistance to yellow rust Puccinia glumarum Erikss. and 
Henn. and resistance to mildew Erysiphe graminis DC. in barley to be a 
simple mendelian recessive. One of his resistant hybrid wheats has 
become of commercial importance and has retained its resistance at 
Cambridge for 16 generations. Nilsson-Ehle (34), in Sweden, corroborated 
Biffen’s findings as to the heritability of resistance to yellow rust, but in 
his crosses he obtained segregates more resistant and more susceptible 
than the parents, which he interpreted as being due to modifying multiple 
factors. Hayes, Parker, and Kurtzweil (75), in America, found the same 
phenomenon in connection with resistance to stemrust Puccinia graminis 
Pers. in wheat and in addition found linkage between resistance and 
certain durum and emmer-like characters. 
Other genera that have been studied genetically in regard to resistance 
to various diseases, in general show the same type of inheritance. 
McRostie (30) ,working with two independent strains of the bean anthrac- 
nose organism Colletotrichum lindemuthianum (Sacc. and Magn.) Bri. 
and Cav., showed resistance to anthracnose to be dominant to suscepti¬ 
bility. When a bean resistant to both strains was crossed on one sus¬ 
ceptible to both, a ratio of 9 resistant to 7 susceptible was obtained in the 
F 2 generation. Either strain alone gave the expected 3 to 1 ratio. Later 
(31) he gave additional data including 36 F s families which supported his 
earlier interpretation. In addition he reported rootrot (caused by 
Fusarium martii phaseoli Burk.,) and mosaic resistance in beans to be 
partially recessive. He interpreted his F 2 results according to the ratio 
9 susceptible to 7 resistant, which was supported by the performance of 
183 F 3 families for rootrot and 329 F 3 families for mosaic. Parker (59) 
published a preliminary report on the crownrust of oats, Puccinia lolii 
avenae McAlpine, in which he concludes that resistance is recessive but 
was caused by multiple factors. Orton ( 36 , 37) described the trans¬ 
ference of wilt resistance of the stock melon to the watermelon by crossing, 
and similarly, resistance to wilt and rootrot was transferred from the 
Iron cowpea to one of the Whippoorwill type. 
Among the farm crop plants that have attained commercial importance 
through their disease-resisting qualities, but which originated by 
selection or introduction, may be mentioned the following: 
1. Upland and Sea Island cotton resistant to wilt. (Webber.) 
2. Potatoes resistant to late blight and scab. (Jones and Stuart.) 
