1890.] PUBLIC DOCUMENT — No. 4. 35 



shell later. That is due, not to the action of the fungus at 

 all, but to a secondary cause, — the attacks of an insect 

 which finds suitable food in the swollen, juicy, succulent 

 tissues of the knot. But in the early stages of the knot, 

 before it is attacked by the insect, you will find a juicy, 

 sappy mass produced by the rapid increase locally of the 

 cells of the young wood and the inner bark, caused by 

 the abnormal stimulation and development produced by the 

 presence of the fungus in the tissues. Finally, along in 

 earl}^ summer, the threads of the fungus penetrate and 

 work their way through the surface of the knot, and their 

 ends stick out all over it, forming a sort of bloom, in 

 appearance to the naked eye very much like the natural 

 bloom of the plum fruit. That bloom is composed, as I 

 have said, of the ends of the fungus threads, which have 

 penetrated the surface of the knot and stand closely packed 

 together all over that surface, like the pile of velvet plush, 

 on a microscopically small scale ; and a little piece of that 

 end gets chopped off, and there is a new spore. That spore, 

 although it is simply the chopped-oif end of one of those 

 threads, has the powder of producing a new fungus, if it falls 

 in a suitable phice, under suitable circumstances of moisture 

 and warmth. These we may call the summer spores. The 

 fungus also produces, as Dr. Fisher says, a second kind of 

 spores, which we may call winter spores. These spores do 

 not get ripe and ready for dissemination until about Feb- 

 ruary or March, and then the threads are formed, not on 

 the surface, like the summer spores, but in the little cavi- 

 ties. By the time they are formed, the juicy interior of 

 the knot has been largely eaten away, and there remains a 

 black crust or scab over almost the entire surface, which 

 may be readily broken down by pressure, on account of the 

 almost entire absence of any solid substance beneath, due 

 to the l)orings of the insect which attacks it. But, if this 

 crust be examined hy the naked eye, or with the aid of a 

 hand lens which magnifies a little, it may be seen that it 

 is filled with little cavities ; and an examination of those 

 cavities would show little elongated sacs, in each of which 

 are eight winter spores. Now, when the spores become 

 fully ripe, they escape through these cavities into the air 



