360 MANUAL OF FRUIT DISEASES 
ceeds to such an extent that the normal form of the limb 
is strikingly changed (Fig. 102). The newly forming knot 
can often be detected in the fall, when it appears as a slight 
swelling (Fig. 100). It is, however, more conspicuous in the 
spring ; at this-time it enlarges and the bark is ruptured, thus ex- 
posing a yellowish surface (Fig. 101). This color does not prevail 
long, but the fungus 
grows to the ex- 
terior and thereon 
develops its sum- 
mer spores which 
give to the knot a 
velvety olivaceous 
appearance. These 
spores are dissemi- 
nated in April, May 
and June, being car- 
ried by the wind to 
suitable places for 
initiating a new 
knot. As the sea- 
son advances the 
gall gradually 
changes color; by 
Fie. 102. — Black-knot; two-year-old knots with the first of Sep- 
black roughened surface. tember black dots 
appear over the 
surface, and within another month the whole knot is perfectly 
black and presents the appearance which is so commonly seen 
(Fig. 102). If one examines such a knot closely, it will be ob- 
served that it is then covered by innumerable small elevations 
which project from its irregular surface (Fig. 102). Each of 
these elevations constitutes a winter condition of the fungus — 
a perithecium in which a second kind of spores develops from 
