474 
Journal of Agricultural Research 
Vol. XXV, No. 12 
dots on the lower leaf surface is the first indication of infection. These 
lesions enlarge and become more or less angular, since they are quite 
sharply delimited by the veins. Meanwhile, the centers of the spots 
become inky black; but the margins retain the water-soaked character 
even at maturity. The centers of old lesions on desiccation become dark 
brown and parchmentlike. The tissues outside the translucent border 
of the lesion become chlorotic, and badly spotted leaves are distinctly 
yellowish. The infections may be so abundant that large, irregular, dead 
areas are formed. There is a tendency for the central tissues of old 
Fig. i. —Deaf of red clover. Trifolium pratense, with bacterial leafe&ot, natural infection. This shows the 
characteristic form, size, and distribution of lesions, both marginal and interior, the latter generally 
intervenous. (Drawing from nature by Charles Drechsler.) 
lesions to crack or to fall away. In consequence, if these lesions are 
marginal, the leaves present a frayed and tom appearance. Abundant 
spotting causes the entire leaflet to become dry or to shed prematurely. 
Under very humid conditions a bacterial exudate may appear on the 
lower leaf surface. This exudate has the appearance of a thin film or of 
small, milky, glistening droplets. If diseased leaves are kept for 12 to 
24 hours in a moist chamber, the bacterial slime will have exuded to 
form larger droplets from which the pathogen may be obtained in pure 
culture. On drying, this exudate becomes a thin, incrusting film. 
