248 FUNGOUS DISEASES OF PLANTS 



XXXVII. DOTHIDIACE^E 



This family includes several hundred species, very few of which, 

 however, are of great importance as disease-producing parasites. 

 It is characterized by asci arising, apparently, for the most part, 

 directly from the stromatic tissue, or at least by a very indistinct 

 perithecium, or perithecial wall. They differ from the Hypocreaceae 

 especially in the color of the stroma, which is dark to black. The 

 most important species, Plowrightia morbosa, black knot of the 

 plum, is discussed at length, but the genus Phyllachora is important 

 from the number of its species and the variety of its hosts. 



XXXVIII. BLACK KNOT OF PLUMS AND CHERRIES 

 Plowrightia morbosa (Schw.) Sacc. 



Beach, S. A. Black Knot of Plum and Cherry. N. Y. Agl. Exp. Sta. Built. 



40: 25-34. J 892. 

 Farlow, W. G. The Black Knot. Bussey Institution, Built. (1876): 440-453. 



pis. 4-6. 

 Halsted, B. D. Destroy the Black Knot of Plum and Cherry Trees. N. J. 



Agl. Exp. Sta. Built. 78 : 1-14. 1891. 

 Humphrey, J. E. The Black Knot of the Plum. Mass. Agl. Exp. Sta. Rept. 



8: 200-2 io. pi. 1. 1890. 

 Lodeman, E. G. Black Knot. Cornell Univ. Agl. Exp. Sta. Built. 81 : 637- 



657. 1894. 



This is one of the most common and most striking fungous 

 diseases of fruit trees in the United States. It has been known 

 and described in orchard literature since the early part of the nine- 

 teenth century, and the causal fungus was described by Schweinitz 

 in 1822. For a long time, however, the knot was commonly 

 supposed to be caused primarily by insects. A considerable litera- 

 ture upon this disease accumulated, but it was not until 1876 that 

 a thoroughly competent account of the fungus and its relation to 

 the knot was presented. This latter account has remained the 

 chief basis of opinions concerning this fungus. 



Geographical. The black knot was apparently at one time con- 

 fined largely to the Atlantic seaboard, and was particularly abundant 

 only in New England and perhaps New York. It is now known 

 to extend across the northern United States to the Pacific Coast, 

 although very large portions of the Southwest and large areas of 



