THE PLUM IN KANSAS. 123 



BLACK-KNOT OF THE PLUM AND CHERRY. 



From Bulletin of the Tennessee Experiment Station. 



The black-knot of the phim and cherry is one of the most striking 

 and familiar of the fungous diseases which attack our cultivated plants. 

 That it is a fungous disease there is no longer any question, although 

 for a long time the trouble was thought by many to be due to the at- 

 tacks of insects. It is a parasitic plant, belonging to the great group 

 of plants called fungi, that causes the development of the black knots, 

 and its characters and habits have been closely studied by mycologists, 

 and are now very well understood. 



In the Eastern and Middle states this disease is of common occur- 

 rence, and is often very destructive. Wild plum and cherry trees are 

 attacked by the disease, and from these it may spread to the culti- 

 vated sorts; the disease may also be carried to new localities by the 

 introduction of unhealthy nursery stock. 



The knots are often very large, and not infrequently they com- 

 pletely surround the branches. The surface of the knots is black, 

 more or less irregular, and free from bark, excepting, perhaps, here 

 and there a fragment which has been carried up with their growth. 

 Around the base of the knots one will find the raised and broken 

 edges of the bark of the branch, showing that they (the knots) origi- 

 nated beneath it. If closely examined, the surface of the mature 

 knots will be seen to be studded with slightly elevated and rounded 

 projections, imparting to it a pimply appearance. Each one of these 

 little pimples rejDresents a fruit of the fungus, which is many, many 

 seeded. 



They have thick, black walls, and at the top of each is a small open- 

 ing through which the seeds, or spores, as the seeds of fungi are called, 

 escape when ripe. In the interior, or cavity formed by the fruit walls, 

 there are a great number of delicate, elongated sacks, and it is within 

 these that the minute sjjores are formed, usually eight in each sack. 

 Each sack is hardly more than one three-hundredth of an inch long 

 or high. The spores, which consist of two cells of very unequal size, 

 are, of course, exceedingly minute. 



The description just given is that of the mature stage in the devel- 

 opment of the fungus. There are other and earlier stages, in which 

 spores or reproductive bodies quite unlike those just described are 

 produced. One kind is borne on dark, olive-green stalks, which, dur- 

 ing the period of their formation, cover the knots so thickly that their 

 surfaces resemble silk plush or velvet. 



Other spores, supposed to belong to this fungus of black-knot, are 



