EXPERIMENT STATION BULLETINS. 



329 



fungicides in preventing blight, but it is quite likely that, if begun in time 

 and persistently followed up, it would greatly reduce the amount of blight. 



CFig. 5. Black Knot. Plowrightia morbosa. Sacc. 

 1. Stem of plum tree with knot upon it, as it appears 

 in the fall and winter. 



2. Perithecium with mycelium, a a between the cells 

 of the stem, and covered with filaments bearing 

 spores, 6, at their extremities. Section made in May. 



3. Filaments and spores, (conidia) more highly 

 magnified. 



4. Section through a cavity containing stylospores. 

 After Farlow. 



42 



BLACK KNOT OF THE PLUM AND 

 CHERRY. 



The plum and cherry trees, both 

 wild and cultivated, are in some 

 parts of the state literally covered 

 with wart-like swellings, caused by 

 the workings of a fungus within the 

 tissues. It attacks the new branches 

 as they appear each spring, and 

 frequently kills the trees. It has 

 just commenced to manifest itself 

 in the principal plum-growing 

 counties, and, if the owners are vig- 

 ilant, the large orchards in the 

 county of Oceana, and at various 

 other points along the western side 

 of the state may escape their 

 ravages. The spores enter the 

 branches during the summer, and, 

 by the following spring, the shoots 

 will be considerably swollen, so 

 that the epidermis cracks, reveal- 

 ing the green bark underneath. 

 During the season, a vast number 

 of spores are produced which serve 

 to scatter the disease. By fall the 

 fungus has completed its growth, 

 and will appear as a shiny, black 

 swelling, with its surface covered 

 with minute dots. The winter spores 

 ripen early in the spring, and 

 are ready to communicate the 

 disease to the young shoots as they 

 develop. 



