298 THE ESSEX NATURALIST
of Volume 6 of "Researches on Fungi" is devoted to
Discomycetes. Buller showed that in many of the larger
species the asci bend towards the light, although they do
not project very far beyond the level of the paraphyses. In
a cup-shaped fruit-body such as that of Peziza vesiculosa
this response of the asci results in the ascus-jets being
directed out of the apothecium—that is to say, towards the
light (Fig. 3). If the asci were not phototropic and the
spores were simply discharged in a direction at right angles
to the surface of the hymenium, there would be a crossfire
of spores, those from one side bombarding the opposite sur-
face. Thus many spores would fail to escape into the
turbulent air above the apothecium. Again, phototropism
of asci is all-important in the escape of spores in the rather
complicated fruit-body of the morel (Morchella). This is
about the largest of the Discomycetes. The apothecium is
not cup-shaped. The hymenial surface, borne on a stalk
4-6 inches high, is highly convoluted so that a number of
rather irregular pits are formed each lined by hymenium.
As with Peziza, if the asci were not phototropic most of the
sticky spores would be wasted by being shot on to the
opposite wall of the pit. As it is, the asci point towards the
light—towards the opening of the pit—so that on discharge
the ascospores are thrown clear. It must not, however, be
supposed that all asci are phototropic. For example, I can
find no evidence of directional response to light in the asci
of Bulgaria inquinans.
The ascus is a turgid cell. and. if it is to fulfil its function
as a spore-gun, its turgidity must be maintained until the
last moment. Thus it is clear that the water supply to the
hymenium is of vital importance for the proper functioning
of cup-fungi. Most cup-fungi, in contrast to the flask-fungi
(Pyrenomycetes), have no power of enduring drought. They
are mostly fleshy forms which can function only if condi-
tions are reasonably damp. If they dry, subsequent revival
is impossible. The difficulty of maintaining the asci in a
turgid condition is increased by the fact that water con-
duction through the mycelium of septate fungi is apparently
rarely able to make good any considerable loss by trans-
piration. One example of water conduction making good
such loss is. however, seen in Mitrula phalloides. This
fungus is aquatic in its vegetative growth. The mycelium