1876.] The Black Knot. 343 
“ With a hand-lens one can see small hemispherical protuber- 
ances, which are the beginnings of the ‘ perithecia.’ The whole 
surface of the protuberances is covered with filaments (Plate III., 
Figure 2) about .04 mm. to .06 mm. in height and .004 mm. in 
breadth, which are somewhat flexuous and frequently divided by 
cross-partitions. The filaments are more frequently simple, but 
sometimes branch. At the tip of the terminal joint, or more fre- 
quently a little to one side, is borne a spore .006 mm. in length, 
ovate and rather sharply pointed at the lower end. Not unfre- 
quently two or three spores are borne on the upper joint, and 
others may also be produced on some of the lower joints. We 
have never seen any cross divisions in the conidial spores, which 
fall very early from their attachments. The conidia which we 
have just described spring directly from the surface of the peri- 
thecia, They continue to bear their spores until the latter part 
of summer, when they begin to dry up, and as winter sets in 
one finds only their shriveled remains.” As autumn approaches, 
the knots assume their black color, the inner portions being 
either destroyed by insects or reduced to a powdery mass, with 
only the hard outer shell, which contains the perithecia, left in 
place. These perithecia are small pits or sacs which are scat- 
tered through the hard crust and contain the sexual spores, borne, 
always to the number of eight, in asci or cells. In Plate IV., 
- Figure 4, is shown a highly magnified cross section through a 
perithecium, with the spore sacs attached to the wall. Figure 3 
of the same plate gives a still more magnified view of two of the 
asci, with the spores somewhat regularly disposed ; while spring- 
ing from the wall of the perithecium and extending above the 
asci are the long and slender sterile threads called “ paraphyses.” 
“ The asci grow slowly during the winter, and about the middle 
of January the spores begin to ripen. In the month of February 
they are found in perfection; but late in spring they are not so 
abundant or in such good condition. We first found a few ripe 
Spores on the 17th of J anuary ; and in the second week of Feb- 
ruary, most of the knots examined contained ripe spores. .... 
The spores measure from .016 mm. to .02 mm. in length and 
from .008 mm. to .01 mm. in breadth. They are two-parted, as 
Shown in Plate IV., Figures 5 and 6; one division being uni- 
formly much smaller than the other, and not more than one 
quarter or one third as long. The spores are transparent and 
slightly granular. As they lie in the ascus, the small end almost 
‘variably points downwards. Spores which ripen in February 
