316 Wisconsin State Hobticultujral Society. 



branches. If the winter spores have begun to form, they go on r 

 and ripen, even if the knots are cut from the trees, notwithstand- 

 ing they may be exposed to a great degree of cold. Knowing 

 this, we can infer that it will be'safer to burn all knots which are 

 removed. 



The black knot is unknown in Europe, although the European 

 cultivated plums and cherries are botanically the same as ours. 

 How does it happen, then, that our trees have a disease unknown 

 in Europe? The reason is, that the fungus which causes the dis- 

 ease is a native of America, and grows on our wild plums and 

 cherries. * * * Being a native of America, when plums and 

 cherries were introduced from Europe, the fungus grew upon 

 them as well as upon our own wild species. Its injurious effects 

 are better known on the cultivated plums and cherries, because, 

 being cultivated for their fruit, they are more generally observed 

 than the comparatively worthless wild species. All our wild 

 cherries are not attacked by the fungus, as, for example, the rum 

 cherry, Prunus serolina; and there are a number of cultivated 

 varieties of cherry which are not subject to the disease. In at- 

 tempting to check the disease, one should not forget to remove the 

 knots from the wild cherries growing near orchards, as well as 

 from the cultivated cherries. 



Probably but few of the tumors on trees and shrubs can be said 

 with certainty to be caused by fungi, yet no tumor of any size is 

 probably free from them. The number of species of fungi is 

 enormous, and not a small proportion inhabit dead wood and 

 bark ; and the rough surface of any old tumor forms a suitable 

 place of growth for a great many species. They are, however, 

 not the cause of the knots, but an aftergrowth, and are recognized 

 as such by those who make a special study of fungi. Many 

 tumors are known to be caused by insects, and, as a rule, the dis- 

 tortion produced arises not so much from the attack of the insects 

 themselves as from the effort of the plant cells in succeeding years 

 to perform their normal work. The injury often consists in the in- 

 vasion of a leaf bud by some very small insect, and, as a result 

 of the irritation, the leaves constituting the bud enlarge, become 

 hardened, and often unite into a comparatively solid mass. The 



