170 BOARD OP AGRICULTURE. [Jail., 



color. All this time the threads of the fungus have been increas- 

 ing rapidly; in fact, the swollen substance is made up largely of 

 these threads, and as they develop and become exposed by the 

 rupture of the bark multitudes of the spores form on the ends of 

 filaments. This takes place about the time the plum and cherry 

 trees are in flower. These spores continue to be formed, until 

 midsummer, when a new development begins, which is for the 

 production of the winter spores. As autumn approaches, the 

 black color develops, the outer surface hardens, and frequently the 

 interior soft substance is destroyed by insects, and only a shell re- 

 mains. In this crust are small nodules or protuberances, on the 

 inside of which a multitude of small sacs are attached. These 

 spores are not fully developed until very late in the season. The 

 choke cherry [Prunus Virginiana), is a favorite home for the black 

 knot, as the neglected fence rows in winter show. Next to the 

 choke cherry, in the severity of its attacks, are the cultivated va- 

 rieties of cherries and plums. '• The Morello cherry is more sus- 

 ceptible than any other variety, and next in order comes the 

 Mazzard." Some varieties are free from the knot. 



Remedtj. — Like all troubles caused by fungi, the black knot is 

 contagious, and is propagated by the millions of spores it produces, 

 one crop of which is developed through the spring and summer, 

 and the other in the late autumn. The knife is the remedy. Cut 

 off the knots, wherever and whenever found, and burn them. 

 This can best be done in autumn, after the leaves have fallen, and 

 the knots are exposed to view. The choke cherry bushes and 

 trees might better be cleared away entirely, if situated near plum 

 or cherry orchards. 



The Apple-Leaf Fungus — (^Rcestelia cancellata). 



Observing upon a neighbor's apple tree leaves that were turning 

 crimson in spots, I picked some for examination. A friend, no- 

 ticing the spots, remarked that he supposed " there would be 

 swarms of insects coming out of those blotches before long." De- 

 formities of plants are no doubt generally ascribed to insects, and 

 very naturally, as in many cases the abnormal growths, such as 

 the various galls, oak-apples, etc., are caused by insect stings. 

 There seem to be three general classes of diseases, or troubles, 

 among plants: \. Those caused by insects, and therefore of ani- 

 mal origin. 2. Those which arise from vegetable parasites, the 



