Fan ار ہہک ہے‎ er pe E SET TH 
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SPORE DISSEMINATION 25 
ferent elevations. If the apex of the uppermost ascus be placed on 
a certain mark on one side of the micrometer scale, it will be found 
to move slowly but very uniformly toward the ostiolum. The 
most prominent part of the ascus is the mass of dark spores which 
like those of the other preparation follow the apex in the same rela- 
tive position as in the unexpanded normal ascus. Careful manipu- 
lation of the light will enable one to trace the outline of the entire 
ascus wall, however, as far down as the tops of the unstretched 
asci. This is facilitated by the fact that in stretching, the asci force 
the paraphyses which fill the upper portion of the perithecium into 
a smaller space, causing a difference in refraction between the ascus 
and the surrounding region—the space within the greatly expanded 
ascus appearing more homogeneous and less opaque than that im- 
mediately surrounding it. On account of the darkened character 
of the region immediately surrounding the ostiolum, the progress 
of the apex of the ascus can not be followed for a short distance in 
the average perithecium ; but whena good culture is at hand which 
has been developed in a moist chamber in a moderately lighted room, 
perithecia can be selected with very slight blackening of the apex. 
In these the stretching ascus can be under continuous observation. 
When the apex of the ascus reaches the ostiolum it extends out- 
ward but a short distance. In all cases observed the upper spore 
always protrudes, but it never clears the opening before the ascus 
ruptures and forces the spores out. In the species studied most 
carefully, P. curvula and P. minuta, the break in the ascus always 
occurs between the non-stretching apex and the elastic lateral 
walls. In this way a thimble-shaped portion of the ascus apex is 
cut off. 
The separation may be complete when the thimble-shaped 
apex is pushed forward with the spores, or partial when it remains 
attached to the ascus by one side or becomes rubbed off when the 
old wall contracts and goes back into the perithecium. It must 
be remembered that the ascus remains attached all the time that 
it is stretching ; and that after rupturing the elastic walls contract 
to approximately their normal length again. Woronin was the 
first to offer an explanation of the fate of the old ascus wall. 
That it goes back into the perithecium again there is no question, 
but after twenty or thirty asci have been seen to erupt, it is with 
