302
THE ESSEX NATURALIST
dead submerged Phragmites stalks three Cup Fungi, Niptera
pulla, Belonidium rhenopalaticum and Belonium excelsius,
are very commonly found. The last species is particularly
common. If one rows a boat on a bright, calm day through
a Phragmites swamp, it is easy to see the little pearly
apothecia of B. excelsius, growing on the lowermost inter-
nodes, to which they are addicted, of the dead in situ reeds
often two feet below normal lake level. Now the point I
am coming to is this. In these submerged aquatic Gup
Fungi, spore discharge occurs just as in terrestrial fungi.
The ascus is a spore-gun which can operate below water as
well as in the air—in striking contrast to the basidium,
which can shoot off its spores only in the air. It is true
that, because of the much greater viscosity of the water as
compared with air, the distance of discharge is much less,
but in the aquatic environment the only essential is that the
spores shall be freed from the parent tissue.
It is natural to ask whether these aquatic Cup Fungi show
any specialisation to the aquatic habitat. The answer seems
to be that, by and large, they do not. However, an excep-
tion may, perhaps, be made for the two closely-similar
genera, Vibrissea and Apostemidium. A not-infrequent
species is Apostemidium guernisaci occurring gregariously
on submerged twigs as sessile apothecia about 1 mm. in
diameter and bright yellow in colour. The discharged spores
are very long (200-800 microns) and narrow (1-2 microns),
and each on liberation assumes an s-shaped form with the
curvature lying in more than one plane. These sigmoid
spores strongly resemble the conidia of such common aquatic
Hyphomycetes as Anguillospora longissima and Flagello-
spora curvula. It seems likely that a long, thread-like dis-
persal unit of this kind is of significance not only because
it does not settle too soon and so stands a better chance of
dispersal, but also because it catches on more readily than
would a spherical or oval one to a suitable substratum on
which it might grow. It is of interest that Zostera, the only
genus of British plants in which pollination occurs below
water, the pollen grains are long and thread-like.
It seems likely that the aquatic Discomycetes have been
derived from terrestrial ancestors, and in going down into
the water little modification has been necessary.