m 



specimens on both the black and white oak in Massachusetts 

 by Mr. R. G. Pierce. It is hoped that this brief description will 

 aid and stimulate further observations and study on this inter- 

 esting tree disease, so that we may have more complete informa- 

 tion as to its range and prevalence. 



EXPLANATION OF PLATES. 



' All of the photographs used for illustrating this bulletin were 

 made under the writers' supervision from specimens collected 

 in Pennsylvania. 



PLATE L 



Fig. 1. — A young Strumella infection of the "amoeboid" type 

 on chestnut oak 3 inches in diameter. The minute black 

 nodules scattered over the surface distinguish this super- 

 ficially from a young chestnut blight lesion. 



Fig. 2. — A semi-diffuse type of infection showing three distinct 

 zones of growth, and the characteristic dark nodules scat- 

 tered over the invaded area. The cut stub of a branch shows 

 at the center, and its lighter peripheral portion indicates 

 the depth tc which the fungus had penetrated the wood. 



PLATE IL 



Fig. 3. — A well-defined canker on red oak 2.5 inches in diameter. 

 The advance of the fungus was checked on the right by a 

 marked formation of callus. In the central part the bark 

 was completely destroyed so as to leave an open wound 

 exposing the wood. (See also Fig. 13 for transverse sec- 

 tion through this canker). 



Fig. 4. — The same specimen shown in Fig. 3 viewed from the 

 opposite surface. The zonal advance of the fungus may be 

 noted. Only a narrow bridge of uninfected tissue remains. 

 (See also Fig. 13). 



