530 THE MONTHLY BULLETIN. 



Distribution of the Disease and Its Relation to Climatic and Other 



Influences. 



There is probably more or less infection of fruit by this fungus in 

 every navel orange district in California. While it is primarily a navel 

 orange di.sease it is occasionally found in other varieties. In the latter, 

 however, it is found only when there is a crack or opening in the peel. 



That this disease is found in Florida oranges also is recorded by H. 

 S. Fawcett, in the appendix to Bulletin 107 of the Florida Experiment 

 Station, as noted in the introduction. 



There seems to be a direct relation between this disease and mois- 

 ture. While the fungus is present in the interior. Fairoaks and Oro- 

 ville, oi'ange districts, so few oranges are affected that the loss is insig- 

 nificant and no attention is given to it. The districts are typical of the 

 hot, dry interior, and have practically no fogs or moisture-laden atmos- 

 phere in the spring and early summer, as the case in the southern 

 orange districts. Coast conditions favor the development of the fungus, 

 the fogs and late showers furnishing the necessary moisture for the 

 germination of the spores which find lodgment in or near the navel. 

 If, however, a spore finds lodgment well into the navel so that it is pro- 

 tected from the warm, dry air of the interior regions, the moisture of 

 the fruit may be sufficient for germination. 



The spring of 1908 in the southern sections was replete with fogs and 

 late rains, and the market for navel oranges from some sections received 

 a severe set-back, due to the high percentage of infection by this dis- 

 ease. 



General Descriptions and Characters of Alternaria citri. 



Mycdinm. — Slender, hyaline or yellowish-hyaline tlu'eads, septate, 

 often constricted at the septa, branched and rebranched, and bearing 

 terminal conidia, singly or in series. 



Walls of the mycelium are rather heavy, cells are generally 3.6 inches 

 in diameter and 9.13 inches long, filled with a granular protoplasm and 

 often contains vacuoles. 



Spores. — Conidia are the only spores produced by this fungus. The 

 young conidia are variously shaped; obovate, oblong-elliptical, or sub- 

 globose. 8.13 inches in diameter by 10.18 inches long, 2-3 celled, very 

 little, if any, constriction at septa, surface smooth, color slightly yel- 

 lowish hyaline to light olivaceous hyaline, occurring singly or two to 

 three catenulate in series. 



Older conidia are short-clavate-oblong, 15.25 inches in diameter by 

 24.40 inches long, 4-12 celled by transverse and longitudinal septa, more 

 or less constricted at septa according to age, each cell when mature being 

 almost spherical, filled Avith granular protoplasm and generally contain- 

 ing vacuoles. The surface is set with irregularly scattered tubercles 

 (Figs. 326 and 327). Conidia often 3-6 catenulate in series arising from 

 a simple or branched pedicel. Occasionally secondary conidia arise 

 directly from the primary, which process has been found to continue 



