SUSCEPTIBILITY TO PARASITISM IN MAIZE 299 
Jesse B. Norton (18), the asparagus rust; L. R. Jones (19), the flax 
wilt; and Gernert with reference to the corn aphis, noted above, all 
find that resistance tends to be shown in the first generation of crosses 
between types which are classed as resistant and susceptible. 
Although resistance is a highly complex and variable character 
there can be no doubt but that many types of resistance are determined 
by definitely inherited factors more or less independent of the envi- 
ronment and of heterosis. There may be certain general principles 
involved in that certain types of disease thrive best in plants which 
are in a luxuriant condition either from environmental causes or from 
the vigor of hybridization. If that were the case resistance would 
tend to be recessive in those plants which show heterosis markedly. 
On the other hand certain other infections may be more pronounced 
in less vigorous plants. In that case heterosis would tend to keep 
the first generation plants free from the attacks so that the resistance 
would seem to be dominant. 
It is doubtful, however, that in the case of the susceptibility of maize 
to the smut fungus, reported here, vigor can be more than a minor 
variating factor. Although the most resistant strain (no. 1-6-1-3) is 
the most vigorous of the four inbred lines, many naturally crossed 
varieties are several times as vigorous and productive and are quite 
susceptible. And there are other inbred strains (nos. 1-9-1-2 and 
1-7-1-2) which are no more vigorous than the most susceptible one 
(no. 1-7-1-1) yet are only slightly susceptible. 
The evidence from these inbred strains of maize and their first 
and second generation hybrids seems conclusive that susceptibility is 
governed by factors which are capable of being segregated into some 
lines and not into others and that the modification of the expression 
of the parasitism by the vigor of the plants is a minor consideration. 
Connecticut Agricultural Experiment Station, 
New Haven, Connecticut 
LITERATURE CITED 
1. Orton, W. A. The Wilt Disease of the Cowpea and Its Control. U. S. Dept. 
Agr. Bur. PI. Ind. Bull. 17, Part I, pp. 9-22. Pis. I-IV. 1902. 
2. The Development of Farm Crops Resistant to Disease. U. S. Dept. 
Agr. Yearbook, pp. 453-464. 1908. 
3. Cotton Wilt. U. S. Dept. Agr., Farmers' Bull. 333, pp. 24. 1910. 
4. Stuart, William. Disease Resistance of Potatoes. Vt. Agr. Exp. Sta. Bull. 
179, pp. 147-183. 1914- 
