370 Harper.—Sexual Reproduction in Pyronema 
by a vegetative layer the particular ascogenous branches that 
come from each pair of sexual organs. 
As in the other forms studied, the ascogenous hyphae are 
relatively transitory structures in their basal portions, and 
maintain no permanent system of connexions for the transfer 
of food from the ascogonium to the developing asci. The 
ascogonium persists longer than do the ascogenous hyphae, 
but it is merely an empty sac. The ascogenous hyphae can 
hardly be found in an old fruit. They have simply collapsed 
from the pressure of the growing vegetative hyphae around 
them. In the sub-hymenial layer the tips of the ascogenous 
hyphae continue to grow and branch until the fertilized 
nuclei are all utilized in forming asci. The collapse of the 
ascogenous hyphae at a relatively early stage indicates that 
it would be quite difficult for the asci to be nourished through 
them from below. The development of the asci is relatively 
slow, and, as I have noted in other cases, all the conditions 
indicate that the asci get their nutriment through their walls 
from the adjacent paraphyses. 
The fact that not all the asci develop simultaneously 
necessitates the continued development of paraphyses from 
the hypothecium to provide for the later-developing asci. 
A special type of hypha has been developed in Pyronema 
to provide these late-developing paraphyses. These hyphae 
arise from the basal cells of the cluster or the stalk-cells 
of the oogonia, and push up among the vegetative hyphae 
of the hypothecium. They then become divided by septa 
into short cells which immediately swell into large spherical 
or barrel-shaped vesicular reservoirs''Vhich, as fast as they 
swell, are packed full of protoplasfri with numerous nuclei. 
This protoplasm is unusually dense. The diameter of the 
reservoir cells is twice or three times that of the ordinary 
hyphae, and altogether they are very conspicuous objects 
(Figs. 23, 24). In free-hand sections not stained to show the 
nuclei one would very naturally pick out these hyphae for 
the ascogenous hyphae. It is easy to prove, however, that 
they contain only vegetative nuclei, and are ultimately de- 
