178 DISEASES OF CULTIVATED PLANTS 



ground should also be collected and burned. All cankers on 

 the branches should also be removed. When on thin shoots 

 the entire shoot should be cut away, in the case of thicker 

 branches, the diseased patches should be cut out, and the 

 wound at once dressed with tar. 



Spray with Bordeaux mixture once before the buds open, 

 and again at intervals until the fruit is almost ripe. 



Berkeley, M. J., Gard. Chron., p. 245 (1S56). 

 Blair, J. C, U.S.A. Expt. Sta. III., Bull. 117 (1907). 

 Schrenk and Spaulding, U.S. Dep. Agr., Bur. PL Intl., 

 Bull. No. 44 (1903). 



Southwonh,y6>//r;/. My col., 6, p. 164. 

 Stoneman, Bot. Gaz., 26, p. 71 (1S98). 



POLYSTIGMA (Pers.) 



Stroma flat, rather fleshy, tawny or reddish ; perithecia 

 immersed; asci 8-spored ; spores elongate, continuous; 

 spermogonia usually present. 



Forming fleshy, flattened, reddish patches on leaves. 



Plum leaf blister. This disease is caused by Poly stigma 

 rubrum (I). C), and attacks cultivated plums and other 

 members of the genus Prunus. It also occurs on almond 

 and white thorn. The leaf i-^ the part injured, the fungus 

 forming somewhat large, dull, orange-red patches, obvious on 

 both surfaces of the leaf, but most pronounced on the lower 

 side, where a flat stroma is formed, which is slightly thicker 

 than the substance of the leaf. The red colour ot the patches 

 is due to the presence of a reddish-orange, oily substance 

 present in the cells of the fungus. With a pocket-lens 

 numerous very fine punctures may be seen on the surface of 

 a blotch ; these are the mouths or openings of globose con- 

 ceptacles sunk in the stroma, and containing spermatia. 

 These spermatia are produced in immense numbers throughout 

 the summer, but experiments have failed to show that they 

 are capable of producing the disease. After diseased leaves 

 have been lying on the ground throughout the winter, an 

 ascigerous condition of the fruit develops in the stroma, 

 which in the meantime has become blackish, hard, and 



