Entomological Notes. 315 



black knot is invariably preceded by the presence of the. fungus 

 known to botanists under the name of Sphceria Morbosa, and the 

 onward growth of the mycelium of the fungus in the healthy 

 stem of the plum is followed without fail by the swelling and 

 blackened characteristic of the knot. On the one hand, we never 

 find the fungus unless accompanied by the knot ; on the other, 

 we never find the knot unless accompanied and also preceded by 

 the fungus. If you examine tbe slightly swollen branches of the 

 Choke-cherry in the spring, before the bark has cracked open, 

 you will find the threads of the fungus already in the stem, and 

 later in the season you will certainly find the characteristic swell- 

 ing and blackening. If the fungus were only found with the 

 knot, we could not say that it was the cause of it. As the knots 

 grow old, there is usually a number of insects and fungi found in 

 or on them ; they cannot, however, be considered the cause of the 

 knot, as they are found in other excrescences as well. It is be- 

 cause the fungus consistently precedes, as well as accompanies the 

 knot, that we are entitled to say that it is the cause of the knot. 

 As to the means to be taken to prevent the spread of the dis- 

 ease: our knowledge of the habits of the fungus throws light upon 

 this point. First, we have seen that the threads of the fungus 

 extend in the stem some inches beyond the knot itself, and these 

 threads will, the next season, be followed by a new knot. Hence, 

 in cutting away the knots, one should cut several inches — to be 

 safe, we will say about ten inches — below tie knot?. The way 

 the disease increases in a plant once attacked is by the onward 

 growth of the mycelium. The next question is, how to prevent 

 its spreading to other trees. The spreading is produced by the 

 growth of the spores, one kind of which ripens in mid-winter, 

 and another in early summer. The spores are all light, and easily 

 blown about, and when they fall upon other trees, germinate by 

 sending out new mj^celial threads, which can enter into the stems 

 upon which they have Mien. The object, then, should be to cut 

 off the knots before the spores are ripe. By cutting in summer 

 we can prevent the maturing of the winter spores; by cutting 

 early in the spring we can prevent the ripening of the conidial 

 spores. It is not enough, however, simply to cut off the diseased 



