344 
Journal of Agricultural Research 
Vol. XIV, No. 9 
vesicles of the subtribe Citrinae. The susceptibility of the plants closely 
related to the genus Citrus is in the following order: Poncirus irifoliata , 
Microcitrus australis , Eremocitrus glauca , Fortunella Hindsii , and For- 
iunella margarita. 
No doubt some of the other species and varieties of the wild relatives 
will prove susceptible when other tests are made with vigorous growing 
plants. 
susceptibility of citrus fruits 
Citrus Hystrix DC. (CPB 7872, seedlings), I, II. 
A little-known group of plants found in the Philippine Islands, where they are 
sometimes used as a stack for Citrus spp. A characteristic plant with very large 
petioles. 
Neither plant (20 inches) was in very good condition for infection; consequently 
Citrus-canker did not develop rapidly. However, spots appeared on the leaves and 
twigs, and some defoliation has resulted. Plants are not quite as susceptible as 
grapefruit. 
The spbts (PI. 52, C) resemble those described on grapefruit in their general char¬ 
acters. 
Citrus Hystrix Wester. “ Cabayao ’ * (CPB 7831, seedling), II. 
A plant similar to the above. Owing to better condition of the plant (20 inches), 
citrus-canker has been much more severe. Apparently it is as susceptible as grape¬ 
fruit. Infections are found on the leaves and twigs and some defoliation has resulted. 
The spots are identical with those on C. Hystrix 7872 (PI. 52, C.). 
Citrus Medica L. Citron of commerce (CPB 7768, cuttings), I, II. 
Both plants (20 inches) pushed out an abundance of new growth while in the cases. 
Citrus-canker spots appeared on the leaves two weeks after the first inoculation. At 
the present time the spots are fairly well distributed over the leaves, and new infections 
are developing weekly. Canker is confined to the leaves and has not caused any 
defoliation. 
The spots (PI. 50, A) are fairly well distributed over the leaf, small, occasionally 
measuring over a millimeter in diameter, with no apparent increase in size. They 
are light brown at first, becoming darker with age. The spots are raised and 
somewhat corky, breaking through the upper surface and appearing flat and com¬ 
pact. The oily outline is distinct and is present only around unbroken spots, 
while the yellow zone is quite wide. 
Several other species of C. Medica gave positive results, the order'of susceptibility 
being as follows: “Etrog” citron 11178, “Sidro” citron 7816, citron of commerce 
7768, “Nana” citron 11281, citron 7836, “Odorata” citron 11294. 
The same type of spot (PI. 50, A) was found on all the plants, and in some cases 
where they were extremely numerous on a leaf caused defoliation. However, owing 
to the small size of the spots, no injury resulted when they were scattered over the 
leaf. The number of spots per leaf does not influence their size. This point is 
important in judging the susceptibility of the citrons. 
Citrus sp. Small lemon (CPB 7833, seedling), II. 
An introduction from the Philippines. 
The new growth has been excellent and consequently in fine shape for infection. 
Citrus-canker appeared on the foliage early in the experiment and has spread very 
rapidly to all the leaves, causing considerable defoliation. Numerous spots are 
present on the upper surface of the leaves. Twig infections are rather severe. The 
plant is extremely susceptible. 
