Aug. 26 ,1918 Susceptibility and Resistance to Citrus-Canker 
351 
Tangelo, Thornton (No. 2) (C. nobilis var. deliciosa, tangerine, X C. grandis, Florida 
grapefruit). 1 (CPB L715A, seedlings), I, II. 
The plants (10 to 12 inches) have not been in the best of condition for infection, 
as growth was slow. Citrus-canker developed shortly after inoculation at the punc¬ 
tures, but did not spread rapidly to the young foliage, so that at the present time 
only a few of the leaves are infected. While the spots (PI. 50, C) are typical of those 
on grapefruit, the hybrid gives some promise of being much more resistant to Citrus- 
canker than grapefruit. 
Tangelo, Sampson. (CPB L789A, seedlings), I, II. 
In many respects these plants (12 inches) were similar to the Thornton tangelo 
in their growth and behavior toward Citrus-canker. 
Tangelo (CPB 1230, seedling), I, 
The plants (14 inches) were in about the same condition for infection as the Thorn¬ 
ton tangelo and appeared to be slightly more susceptible. 
Tangelo (CPB 1257A, seedlings), I, II. 
The plants were similar to tangelo 1230 in growth and susceptibility to canker. 
The spots, like those of the other tangelos, are typical of those described for grape¬ 
fruit. 
The results obtained with the hybrids are extremely interesting and 
instructive. When two susceptible plants are used in hybridizing the 
hybrid shows the same susceptibility as the parents. Good illustrations 
of this are the citranges and cicitranges, citrumelos, and limelos. How¬ 
ever, when an extremely susceptible plant is crossed with a kumquat 
or a mandarin type of orange the hybrid retains to a large extent the 
resistance exhibited by the resistant parent, as illustrated by the be¬ 
havior of the citrangequat, citranguma, citrandarin, and to a less ex¬ 
tent by limequat and tangelos. 
Unfortunately, no hybrids were included in the experiments where 
both parents show marked resistance. 
In the further work of hybridizing for resistance to Citrus-canker the 
parents must be confined for the most part to those plants which show 
marked resistance to canker, especially in the genus Fortunella and C. 
nobilis with its many varieties. 
DISCUSSION OF RESULTS 
The factors necessary for the successful inoculation of the plants in 
these experiments, especially those which were somewhat resistant, are 
a high temperature, a relatively high humidity, and a vigorous and rap¬ 
idly growing plant. Without the inclusion of the last factor only the 
more susceptible plants are infected. It is for this reason that the con¬ 
dition of the plants for infection has been given for each host discussed. 
When the plants were not in good shape for infection, few or no results 
were obtained. In such cases no relative comparisons of susceptibility 
or resistance could be made. 
Under the conditions governing the inoculations, then, the maximum 
amount of infection possible was obtained. No doubt under ordinary 
1 This is not the true Thornton, but a sister variety, differing considerably though resulting from 
the same cross. 
