DISEASES. 191 



guished from the old by its dull, opaque, brown-black 

 color, while the old is coal-black and more or less glossy. 

 When cut into, it is found to be fleshy inside, like an ap- 

 ple, but not juicy, and of a pale greenish-yellow color, 

 with fibres radiating from the axis of the twig, while thd* 

 old Black-knot is internally hard and woody, and of a 

 reddish-brown or rust-red color. The brown-black color 

 of the external surface is retained till the last week in Ju- 

 ly, when the surface of the new Black-knot becomes gradu- 

 ally covered all over with little, coal-black, hemispherical 

 plates^ appearing when viewed through a pocket glass, 

 about the size of the head of a pin, each of these is a dis- 

 tinct fungus, named long ago by Schweinitz { Spfyceria 

 morbosa,? Even on the old Black-knot this fungus may 

 be readily seen, at any time of the year, covering its en- 

 tire surface. So far I have added little to the information 

 already published on this subject, except by the specifica- 

 tion of dates. But in addition to these facts, I discovered 

 that about the last of July or the first week in August, 

 there grows from each fungus on the surface of the Black- 

 knot a little cylindrical filament about one-eighth of an inch 

 long, which no doubt bears the "seed or " spores," as they 

 are technically termed, of the fungus, and that these fila- 

 ments very shortly afterwards fill off and disappear, 

 leaving behind them the hemispherical plates, which alone 

 had been hitherto noticed by the botanists. In another 

 Epiphytous fungus, which grows commonly and abund- 

 antly in Illinois on the Red Cedar, but which differs from 

 the Black-knot in being attached to the twig by a very 

 short stalk or peduncle, and in being roundish and exter- 

 nally of a reddish-brown color instead of elongate and 



