confluens and the Morphology of the Ascocarp. 359 
thick and into this mass the papillae mentioned above as 
forming on the basal region of the oogonium push out (Fig. 19). 
These papillae are the young ascogenous hyphae. On the 
free outer surface of the oogonium many of them arise at 
a higher level than the vegetative hyphae have reached, and 
grow out a short distance free and unenclosed (Figs. 15, 15 a, 
and 17). These branches contain no nuclei at first. 
At the time when the ascogenous hyphae first appear, the 
nuclei are still massed in the centre of the oogonium. As 
soon, however, as the fusion of the majority of the pronuclei 
is complete the dense mass begins to loosen up. This is well 
shown in two sections taken from different parts of the same 
oogonium (Figs. 17 a and b ). At this stage the nuclear 
fusions are practically all complete. The nuclei are rounded 
up and show no trace of the fusions by which they were 
formed except an increase in size in some cases. 
From the completion of the fertilization stage onward, the 
oogonium may be known as an ascogonium. It enters upon 
a renewed stage of vegetative activity which was made 
possible as a result of fertilization. In Pyronema , as we 
have noted, the ascogenous hyphae spring directly from the 
oogonium without its first developing into a multicellular organ 
as in Sphaerotheca and Erysiphe. This is, however, a minor 
difference ; the fact that there is a period of renewed growth 
beginning at the time of fertilization and leading to ascus- 
formation, justifies the retention in all cases of the term 
ascogonium for the body from which the ascogenous hyphae 
spring. The scattering of the nuclei in the ascogonium is 
very rapid, as evidenced by the appearance of fusion-nuclei 
in the young ascogenous hyphae (Figs. 17 a and b) which 
when they were only a trifle shorter contained none (Fig. 15 a). 
It is also very apparent at this stage that the massing of the 
nuclei in the centre of the oogonium was not at all in the 
nature of a fusion. As soon as the fusion in pairs is complete 
each nucleus appears with perfectly sharp contours in the 
loosening mass. The fusion-nuclei at this stage show much 
more conspicuously differentiated nucleoli than did the pro- 
