July 15, 1920 Relative Susceptibility to Citrus-Canker 343 



SUBTWBE LaVANGINAE 



Hesperthusa crenulata Roem. Naibel (CPB 2759, seedlings), II, III, in field, 1917 



and igi8. 



Because the spots produced were so nontypical the susceptibility of these plants 

 was doubted until cankers developed on the twigs and branches. The spots (PI. 59, 

 B) are small and nontypical, although 90 per cent of the new leaves on the plants are 

 infected. On the twigs they are rather numerous, flat, very oily, and apparently 

 ruptured. In the field the few spots formed on the twigs have remained unruptured, 

 very oily, and slightly raised. On the leaves the spots are nontypical, few, and in 

 some cases slightly ruptured. 

 Triphasia trifolia P. Wilson. Lime berry (CPB 2689A and 7780, seedlings), I, II, 



and II, in field, 1918. 



The plants have remained free from canker in both the field and greenhouse. 

 Severinia buxifolia Ten. (CPB 2760, cuttings and seedlings), I, II, in field, 1917, 



1918, and 1919. 



Like Triphasia, the plants are apparently immune. 



SUBTRIBE CiTRINAE 



Citropsis Schweinfurthii Swingle and M. Kellerman. African cherry orange (CPB 



11260, seedlings), I,' II, infield, 1917 and 1918. 



Several small spots have developed along a wound on one leaf, while several small, 

 scattering, and imruptured spots were found on a few young leaves. The spots are 

 typical of those found on Casimiroa edulis. No positive results have been obtained 

 in the field. 

 Atalantia citrioides Pierre. (CPB 7534, cuttings), I, II (2 plants), III, in field, 1918. 



Canker spots first appeared on the plants in experiment I in May, 1918: Since that 

 time all plants have become infected, the spots being well distributed over the new 

 foliage. 



The spots (PI. 59, A) are small to medium, of a brick color, round, flat, and sometimes 

 breaking out in a corky mass. Only a slight depression is visible on the upper surface. 

 The oily outline is very distinct, and no yellow margin is present. The spots are some- 

 what similar to those described for Chaetospermum , and the plants are almost as sus- 

 ceptible. During 1918 no positive results were obtained on the few plants in the 

 field. 

 Atalantia ceylonica Oliver {Rissoa ceylonica, Am.). (CPB 11225, seedling), III. 



A few oily spots (PI. 59, A, center) have been produced on all the leaves of the plant. 

 They are present also on the twigs. The spots are identical with those described on 

 A . citrioides, although the plant is slightly more susceptible. 



Poncirus trifoliata (L.) Raf. {Citrus trifoliata L.). Trifoliate orange (Seedlings, Ala- 

 bama), I, II, III, infield, 1917. 



All the plants (PI. 65, A) included in the experiments have proved to be extremely 

 susceptible in both the field and the greenhouse. In experiment III the plant was 

 killed outright by the heavy canker infection. Leaves, thorns, twigs, branches, and 

 even the old wood were attacked. As a rule, all the spots on the leaves are small to 

 medium sized and very numerous, while on the stem they are large, girdling, and 

 corky. 



Poncirus trifoliata is extremely susceptible and therefore will always be a menace 

 to complete eradication of canker in Alabama, especially since it has been found 



J Ircluded in experiments of March 21, 1918. 



