358 Harper.—Sexual Reproduction in Pyronema 
covered. This inequality in the distribution of the enveloping 
hyphae may continue through their entire development. As 
they become more numerous in most cases they gradually 
spread around the base of the oogonium for about one-third 
of its height, leaving still exposed a large oblique circular 
segment of its surface. As a result of this habit of growth 
we have in the mature fruit-body a series of these exposed 
oogonial surfaces bulging out around its base, enclosed by 
a fibrous network of the vegetative hyphae. Sections of the 
fruits of course show these exposed oogonial surfaces only when 
they lie in a plane cutting such an exposed surface in a radial 
direction (Fig. 23 to the left). In other cases the sections 
may show the oogonia entirely (Fig. 20), and in some cases 
equally enclosed on all sides. In old fruits the secondary 
mycelium, as described below, forms a more or less perfect 
envelope around all these structures. 
The vegetative hyphae developing in connexion with each 
of the whole number of oogonia of a cluster, whatever it may 
be, become combined in a single apothecial fruit-body as has 
been observed by all the earlier investigators of Pyronema. 
Such an ascocarp has been called a compound apothecium 
or syncarpium as compared with the ascocarp of Erysiphe 
which develops from a single ascogonium. Very frequently 
the rosettes of sexual organs grow so close together that 
further combination occurs by contact of adjacent ascocarps so 
that crusts or turfs of considerable extent may be formed. 
It is, however, by no means unusual to find single isolated 
pairs of sexual cells and from these equally perfect simple 
apothecia develop. These simple apothecia are not, however, 
symmetrically developed around the original axis of growth 
of the oogonium. The vegetative hyphae always develop on 
one side of the oogonium so that a portion of one side of the 
latter is exposed near the base of the hypothecium just as in 
the case of the compound fruits. 
At an early stage (Fig. 14) the vegetative enveloping hyphae 
have enclosed the oogonium quite fully on all but a portion of 
its outer and upper surface. The hyphae are several layers 
