17 ’ 6 Lee: Black Spot of Citrus Fruits 639 
Inoculation experiments have been repeated several times since 
these original results and always, under moderately humid con- 
ditions, a reasonable percentage of positive results was produced. 
THE FUNGUS IN CULTURE 
The fungus grows slowly on the artificial media tried, and is 
not always easily isolated because of the ease with which sec- 
ondary fungi may outgrow it. Beef agar -j- 1, glucose agar 
+ 1, and potato plugs have been used for culturing this fungus ; 
on all of them the fungus makes a restricted growth. The early 
mycelium is grayish, but the colony soon becomes dead black due 
to the formation of pycnidia ; the colonies are small and restricted 
(Plates 3 and 4). Pycnidia appear within six or seven days 
after planting and are abundant, black, spherical, and with pores 
indistinct. 
Under the microscope the young hyphae are hyaline and dis- 
tantly septate, but with age the hyphae become dark olive brown, 
closely septate, and twisted and swollen. Spores are borne 
apically on slender, hyaline conidiophores, and are hyaline, single- 
celled, smooth and thin-walled, ovate, sometimes becoming almost 
pyriform, noticeably granular (Plate 4, fig. 2) ; from cultures 
they vary in size from 9.25 to 12.25 X 5.5 to 8.1 n- Spores are 
not formed profusely. The diagnostic features are the black, 
carbonaceous, restricted growth in culture and the thin-walled, 
granular, and somewhat individualistic spores. The best deter- 
mination of the fungus is its pathogenicity on sweet oranges 
which may be visible in from fifteen to twenty days. The fungus 
agrees closely with McAlpine’s excellent description of Phoma 
citricarpa, and we consider it identical. 
HOSTS 
McAlpine describes this black-spot disease on oranges, lemons, 
and mandarin oranges. The writer’s inoculations on lemons in 
Manila have always resulted negatively; for such experiments 
mature California lemons were used, probably the Lisbon or 
Eureka variety or both, purchased in the Manila markets. It 
may be that these California varieties are not so susceptible 
as are those grown in Australia. The writer is of the opinion, 
however, that Manila temperatures are somewhat above the 
optimum desirable for this fungus, and that inoculations at lower 
temperatures might produce different results on lemons. Man- 
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