Graves: Large Leaf Spot of Chestnut and Oak 171 



circular spots, from 1-2 cm. in diameter, on apparently healthy 

 leaves. These spots are usually pale, with a darker line around 

 the margin, and vary in different specimens between shades of 

 yellow, gray, or red-brown. As the disease advances, concentric 

 zones are added to the original diseased spot, each succeeding 

 zone of the same nature as the original area, i. e., with a darker 

 margin bordering an interior paler area. Thus, at length, large 

 circular spots are formed, composed of concentric, circular bands. 

 (PI. 69, fig. 4, and text fig. la.), These large spots often 



Fig. I. a. Leaf of Castanea dentata showing large leaf spot. X i. b.. 

 Spores of Monochaetia Desmazierii Sacc. X 600, 



measure 5 or 6 cm. in diameter, stretching across the entire width 

 of the leaf. Several large spots occurring on a single leaf may 

 join each other, and the whole tissue in the distal portion of the 

 leaf may thus be killed. Often, in this way, over half of the leaf 

 may be killed. The zones are generally more clearly delineated 

 on the upper surface of the leaf. The under side of the leaf has 

 a whitish mouldy character on the margin of the diseased area, 

 due to a projecting growth of the mycelium. 



