Perithecium of Poly stigma rub nun, DC. 765 
Perithecium. This structure, though not in structural connexion with 
the ascogonium, arises in its neighbourhood, one perithecium being usually 
found in association with each ascogonium. The perithecium is first to be 
distinguished as a group of special hyphae which arise from the small-celled 
hyphae surrounding the ascogonium. These special hyphae are characterized 
by their long finger- like shape ; together they soon take the form of a coni- 
cal mass with its apex pointed towards the lower epidermis (Figs. 17 and 18). 
Their cells may have the nuclei arranged in pairs (Fig. 18). This conical 
mass increases in size and develops into the flask-shaped perithecium 
(Fig. 24). During the early stages of development the disorganizing cells 
of the ascogonium can be clearly seen at its periphery (Figs. 77, 18, and 19). 
At a stage a little later than that shown in Fig. 18, ascogenous hyphae 
become differentiated towards the base of the young perithecium. They 
have no connexion with the ascogonia, but arise by differentiation from the 
perithecial hyphae, which are of vegetative origin as described above. The 
ascogenous hyphae are at first not very sharply marked, but later they are 
easily distinguished by their larger size, denser contents, and larger nuclei 
(Fig. 19). If a section be taken through the base of the perithecium at 
a time when the ascogenous hyphae are differentiating there may be seen 
(Figs. 20 and 21), besides the nuclei in pairs mentioned earlier, larger nuclei. 
Nuclei in close contact are also seen, and in one case what appeared to be 
a stage of nuclear fusion (marked thus * in Fig. 20). There are thus indica- 
tions that at this stage a nuclear fusion occurs which replaces a normal 
sexual fusion now lost. 
The details of the formation of the asci and the ascospores were not 
followed, since for such work this form is not a favourable object, but a few 
stages were observed showing that the ascus is formed in the normal way 
with fusion of nuclei in the penultimate cell of an ascogenous hypha 
(Figs. 22 and 23). 
Conclusion. 
Polystigma rttbrum possesses well-marked, coiled, multicellular asco- 
gonia. The ascogonia disorganize without producing ascogenous hyphae. 
The spermatia also are functionless, and appear in some cases to show signs 
of nuclear disorganization while still within the spermogonia. The asco- 
genous hyphae arise near the ascogonia by differentiation from vegetative 
hyphae. There is a nuclear fusion in the ascus, and some evidence for an 
earlier nuclear fusion in the ascogenous hyphae at the time of their differen- 
tiation. Vegetative hyphae push through the stomata, but there are no 
trichogynes. 
The divergence from the results obtained by Frank and Fisch are no 
doubt to be explained by the deficiencies of the primitive technique 
employed by earlier investigators. 
