Aug. 26,1918 Susceptibility and Resistance to Citrus-Canker 
345 
The spots are very numerous, small to large, light brown, raised, compact, spread¬ 
ing, and corky. The spots break through to the upper surface and are raised, corky, 
and spreading. Oily outline is distinct, while the width of the yellow zone varies. 
Very much like spots (PL 50, B) on grapefruit in general character. Spots different 
from those on citron in a number of particulars, but especially in size and appear¬ 
ance on upper surface. 
Citrus sp. Sweet lemon (CPB 1158, seedlings), I, II. 
An introduction from Jaffa, Palestine. 
Both plants (16 inches) have been in fine condition for infection. Citrus-canker 
appeared on the foliage shortly after the first inoculation and has spread rapidly. 
Infections occurred on both surfaces of the leaves, and on the twigs and the thorns. 
It has caused defoliation of the more badly infected leaves. The plants are 
extremely susceptible. 
The spots (PI. 53, H) are very numerous, small to medium size, light-brown to 
brown, raised, more or less compact, with some cork. The spots cause a dead 
depressed area on the upper surface, but do not break through. An oily outline is 
present, while the yellow zone is indistinct, except when the spots coalesce. The 
spots are like those on citron except in size. 
Citrus sp. "Davao lemon” (CPB 7837, seedling), II. 
An introduction from the Philippines. 
The leaves of this plant (18 inches) have the texture of citron leaves, with the 
shape and petiole of lemon leaves. The new growth has been fine, and in excellent 
shape for infection. Citrus-canker appeared early in the experiment and has spread 
rather rapidly over the foliage, so that infection has been rather heavy. The plant 
is susceptible to a marked degree, although not so much as some of the other lemons. 
The character of the spots (PL 53, I) is like that on the citron except in size. This 
may be expected, owing to the citron-like texture of the leaf. 
Citrus sp. Limon real 18 (CPB 7819, seedling), II. 
The leaves of this plant (18 inches) have the texture of citron leaves, with the 
shape and petiole of lemon leaves. The new growth has been fine, and was in 
excellent shape for infection. Citrus-canker appeared early in the experiment, 
and has spread rather rapidly over the foliage, so that infection has been rather heavy. 
The plant is susceptible to a marked degree, although not so much as some of the 
other lemons. 
The character of the spots (Pl. 50, D) are like those on the citron. This may be 
expected, owing to the citron-like texture of the leaf. 
Citrus sp.(?). Ichang lemon (CPB 11291, seedling), II. 
Introduction from Hankow, China. 
Judging from the character of the leaves, this is not a true lemon, but possibly is 
a hybrid. The leaves are dark green, smooth, pointed at the apex, with a large 
winged petiole. Occasionally a small leaflet arises from the point of union between 
the leaf and petiole. More or less pummelo-like in character. 
The plant (10 inches) has been in good shape for infection. Citrus-canker appeared 
early in the experiment and spread rather rapidly. This plant is about as sus¬ 
ceptible as grapefruit. 
The spots are not numerous, but large, light brown, slightly raised, spreading, 
with cork present, breaking through the upper surface, forming a flat, spreading, 
compact spot. The oily outline is quite distinct, and the yellow zone is con¬ 
spicuous. The spots are typical of those found on grapefruit leaves (Pl. 50, B). 
