24 NORTH AMERICAN SORDARIACEAE 
If a fully mature perithecium of one of the first groups men- 
tioned above be carefully removed from the substratum, and 
mounted in the ordinary way in a drop of water, no difficulty will 
be experienced in recognizing that the asci stand at different levels 
—they are not all the same length. On the other hand an imma- 
ture perithecium when examined in the same way will have all 
the asci of approximately the same length, and all of them will 
extend upward about one third of the length of the perithecium. 
If examined at the proper time the asci and spores will occupy a 
short cylindrical space in the center of the perithecium and appear 
black and opaque. Pressure placed on the cover-glass in either 
of these two cases will cause the perithecial wall to burst and 
allow the asci and paraphyses to escape in a bunch through the 
side or bottom. Never by this kind of rough treatment do the 
asci escape through the ostiolum. On the contrary a break oc- 
curs in the wall ator below the middle, allowing the escape of not 
only the organs mentioned above, but also of a quantity of ascoge- 
nous tissue as well. There is a line of easy separation between 
the ascogenous tissue and the outer wall of the perithecium, which 
gives away and allows the escape of asci and long paraphyses 
which surround them more or less attached together. After be- 
ing removed from the perithecium in this way, the asci change 
their shape very materially ina short time. Instead of maintain- 
ing the normal cylindrical or clavate outline they will become very 
wide and sac-like without an appreciable stipe in P. curvula and 
closely allied species, but with a very long narrow stipe in P. zygo- 
spora. An examination of the apex of the ascus in nearly every case 
will reveal the fact that it does not materially changeits shape. The 
portion of the ascus wall which stretches is, therefore, that which 
lies below a thimble-shaped portion of the apex. Another phe- 
nomenon to be noted here is the constant attachment of the spore 
mass, together with whatever protoplasmic content the ascus may 
have, to the apex of the ascus. In examinations of this kind the 
asci are lying horizontal in water, and the spores as observed fol- 
low the apex of the prolonging ascus. More will be said about 
this phenomenon later. 
Returning now to the mature unruptured perithecium mounted 
in water under a cover-slip, we note again that the asci are at dif- 
