128 
Journal of Agricultural Reseatch 
Vol. XXI, No. a 
especially destructive effect of the disease among seedlings lias also been 
noted in the greenhouse. 
The leaf lesions are not easily differentiated from Septoria lesions, and 
it is likely that leaf infection has not been previously detected because 
of its similarity to Septoria leafspot. Bacterial spot can be recognized, 
however, by its jet black center, greasy upper surface, less circular out¬ 
line, sharp translucent margin, and lack of pycnidia. There is more 
abundant infection of young foliage from bacterial spot. 
A somewhat different type of leaf infection lias been secured by atom¬ 
izer inoculation under greenhouse conditions. Such lesions first appear 
as small, circular, slightly water-soaked spots, i to 2 mm. in diameter. 
These are at first visible only on one leaf surface and are very incon¬ 
spicuous except as viewed in transmitted light, in which case they appear 
translucent. These lesions soon become visible on both leaf surfaces as 
circular, water-soaked or blackish, translucent, greasy spots which remain 
small on old leaves (PI. 26, D). On young leaves such lesions enlarge 
to irregularly circular, dark brown to black spots of a diameter of 3 to 4 
mm. with yellowish or translucent margins (PI. 26, C). Under green¬ 
house conditions the lesions exhibit no tendency to be delimited by veins. 
In the early stages of a leaf lesion under very humid conditions in the 
greenhouse the lower epidermis is puffed up by the bacterial mass under¬ 
neath. A greasy exudate is formed on both upper and lower surfaces, 
and occasionally amber droplets of exudate are formed on the lower 
surface. Tater the central tissue collapses, and on the old leaves the 
spots appear sharply sunken on the lower epidermis and under a binocu¬ 
lar microscope resemble minute circular pits or depressions with fim¬ 
briate margins. About the margin there is a black lacelike discolora¬ 
tion in the tissue due to the intercellular advance invasion. In large 
lesions on younger leaves the centers become dry and parchmentlike 
and show a very distinct dark lacelike pattern when viewed in trans¬ 
mitted light. These parchmentlike centers are usually brown or tan 
colored, translucent, and have dark, irregularly circular margins (PI. 
25, A; 26, B). Such lesions tend to crack at the center. 
Thick-set incipient infection resulting from atomizer inoculation 
may produce large yellow patches on old leaves which become dry, 
dead areas. Coalescence of lesions may cause the disfiguration and 
death of young leaflets (PI. 26, A). Infection of very young, growing 
parts also causes extreme distortion, especially infection of the racliis, 
petiolule, and leaf margin (PI. 26, A). 
Cotyledon lesions are usually very small, craterlike pits or depres¬ 
sions, with an irregular margin, and are often gray or silvery in color. 
As long as a cotyledon remains green a lesion is apt to be visible on 
only one surface, although lesions may occur on either surface. When 
the cotyledon becomes older the lesions become visible from the other 
surface as dark, lead-colored spots. Badly infected cotyledons turn 
