350 Journal of Agricultural Research voi. xix, no. s 



The spots resemble those on grapefruit leaves (PI. 62), but the plants rank with 

 the lemons in susceptibility to canker. 

 Citrus aurantifolia (Auct.) Swingle (C. Umetta Auct., not Risso). Sour lime (CPB 



7338, seedlings), I, II. 



Only a small percentage of the leaves are infected with canker. The spots are also 

 very small and scattering. No twig or stem infections have ever developed. 



The spots (PI. 60, E) resemble those on citron to some extent. However, they are 

 smaller, more compact, less corky, and darker in color. While the plants are rather 

 easily infected, the spots increase slowly in size and are few in number. The sour 

 lime is much more resistant than either the citrons or lemons, almost approaching 

 Satsuma in resistance. Lee (j) reports that the limes, with the possible exception 

 of the "Tahiti," are very susceptible in the Philippines. 

 Citrus grandis (L.) Osbeck (C. decumana L.). Grapefruit (CPB 11170, 7834 and 



Duncan (Alabama), seedlings), I, II; I, II; and II, III. Grapefruit (Duncan 



budded on Poncirus trifoliata), I, II. Chinese ptimmelo (CPB iio6r, seedlings), 



I, III. Hirado Buntan(?) pummelo (CPB 7993, seedlings), I, II. Indian pum- 



melo (CPB 11166 and 2968A, seedlings), I, III, and I, III. Siamese pummelo 



(CPB 11201 and 6111, seedlings and on C. Schweinfurthii), I, III, and II. 



With possibly two exceptions, all the grapefruit plants tested in the greenhouse 

 have proved to be extremely susceptible. Approximately 100 per cent leaf infection 

 occurred, with considerable defoliation. Twig and stem infections were also severe, 

 the spots being large and of a giMling type. Several shoots have been killed by the 

 girdling spots. 



The "Hirado Btintan," reported very susceptible in the preliminary report, has 

 stood up very well, and at the November, 1918, reading only 5 to 10 per cent of the 

 leaves were infected, with few or no spots on the twigs. The Siamese pummelo, 

 especially the number budded on Citropsis Schweinfurthii, shows some resistance to 

 canker. 



In the field, severe infections have been obtained on grapefruit seedlings (1919), 

 grapefruit (Duncan) budded on Poncirus trifoliata (1917), Sullivan grapefruit (CPB 

 iiooi and 11054) (1918), Mark's Chinese pummelo (CPB 11061, 11217F, and 11217G) 

 (1918), Roeding's Indian pummelo (CPB 2 968 A and 11166) (1918), Florida Shaddock 

 (CPB 11255) (1918), Orangedale Chinese pummelo (CPB 11212 U) (1918), French 

 Martin's Chinese pummelo (CPB 11213 J) (1919), and pummelo (CPB 11219 I) (1918). 

 (See PI. 62.) 



Only slight leaf infections have been obtained on the Hirado Buntan pummelo 

 (CPB 7993 and 11021) and recently on the Siamese pummelo (CPB 11201 and 61 11) 

 although these plants have been in the isolation field for the past two seasons and 

 surrounded by badly infected plants. 



Mr. Swingle reports that in Japan the Hirado Buntan is quite resistant, whereas 

 Lee (j) states that the Siamese pummelo is the only variety of Citrus grandis tested 

 by him which gives any promise of being resistant. 

 Citrus sinensis Osbeck (C. Aurantium Loiu*. and Auct. not Linn.). Grenadine 



orange (CPB 7773, seedlings), I, ^ III. Parson Brown orange (CPB 11324, seedlings), 



I,^ III. "Naranja" (CPB 7929, seedlings), II, in field, 1918. Orange (CPB 66A 

 seedlings), I, ' III. 



With the exception of a few small, scattering spots on the twigs of two plants, 

 canker is limited to the foliage of the plants in this group. Apparently the Parson 

 Brown orange is the most susceptible, followed by CPB 66A. The "Naranja " and 

 Grenadine oranges are somewhat more resistant in that only a small percentage of 

 the leaves are infected, the spots are fewer and smaller, and no twig infections are 

 present. 



' Incluaed in experiments of March 21, 1918. 



