226 REPRODUCTION, VEGETABLE (Vegetable Ovum).
sistence and of a dark-brown colour ; the other
white and opaque. The former, which cor-
Fig. 145.
(A
Section of part of the receptacle of a Truffle, about
250 diam.
a, outer layer of the peridium consisting of a
resistant tissue of thick-walled cells ; b, inner layer
of the same, formed of filamentous tissue continu¬
ous with that of v, one of the venæ intemæ, or par¬
titions by which the compartments (originally
cavities) of the truffie are bounded. Portions of
two- of these compartments are seen with the thecæ
and septate filaments which they contain.
responds to the partitions which, in the young
state of the truffle, separated the cavities, is
continuous with the external tissue which
composes the envelope or peridium, and con¬
stitutes the vena internæ of Vittadini.* The
laminae which it forms, consist of filaments
running, for the most part, parallel to each
other. The white substance which occupies
the original cavities of the tuber, is formed
of closed tubes, which are given off in great
numbers from the surfaces of the laminae.
These tubes, which are the terminations of
the filaments of which the laminae are com¬
posed, are of two kinds. Some are of equal
diameter throughout, and divided at intervals
by septa ; others, much shorter, are dilated at
their extremities, and contain spores (thecae).
Each theca is an obovate vesicle, and con¬
tains two, three, or more spores, never more
than eight. Each spore is invested with a beau¬
tifully reticulate, or sometimes warty epispore,
within which may be distinguished a smooth
inner membrane, immediately enclosing the
oleaginous contents.-)-
* Vittadini, Monog. Tuberacearum, p. 2. et seq.
f L. It. & C. Tulasne, Histoire des Champignons
hypogeés, 41-50.
37. Theascophorous Fungi are represented
in their simplest form by the Uredineae, a
family which has been studied by numerous
observers on account of the destructive pro¬
perties of the plants belonging to it. The
mass which is formed by the growth of the
reproductive organs of Uredo under the epi¬
dermis of the leaves of the plants upon which
it grows parasitically, may be aptly compared
to a pustule, a grumous-looking substance,
occupying, as it were, the place of the pus.
On more minute examination of the cavity,
we find that it is bounded by a kind of irre¬
gular wall or lining of pyriform cells, the
smaller ends of which rest upon a reticular
cushion of mycelium. These are probably the
enlarged extremities of the mycelium filaments,
with which many of them can be distinctly
traced to be connected. Towards the base of
the cavity other cells are developed, resem¬
bling those first mentioned in their general
form, as well as in their relation to the myce¬
lium. In these, however, the membrane is
produced inferiorly, so as to form a tubular
pedicle ; while in the club-shaped upper ex¬
tremity it is lined by a considerable deposit of
granular protoplasma, so that here the central
cavity is very much smaller than that of the
external membrane. It is in this cavity that
the spore is formed, at first not exceeding it
in size, but afterwards increasing at the ex¬
pense of the protoplasma, so as almost to fill
the theca. In other genera, as in Phragmidium,
there are pedicled cells of a similar form, and
originating in a similar manner, which, how¬
ever, instead of one spore, develop a number
in their interior ; these spores are arranged in
linear series, and are formed in the same
manner. The protoplasma, however, never
disappears completely, but remains as a more
or less consistent membrane, glueing the ripe
spore to the spore-case which encloses it.
Some of the Uredineae possess a cyst which re¬
minds us of the perithecium of the Sphœriaceæ,
to which they are evidently closely related.
The cyst is formed (Œcidium) of a single
layer of roundish cells.*
38. From the Uredineae we pass by a natural
transition to the Discomycetes and Pyreno-
mycetes. These plants have been investi¬
gated with much success by MM. Tulasne,
who have shown that they possess the
closest relationship not only to the Lichens,
but to the most simple thread Fungi. The
very remarkable facts which these observers
have discovered, render the study of these
plants more satisfactory and instructive than
that of any other family of the class. The
Pyrenomycetes are represented by Sphoeria,
the receptacle of which consists, as is well
known, of a spherical cyst, which is open
above. Its wall is frequently prolonged up¬
wards into a tubular beak, which projects
beyond the surface of the bark or wood in
which the whole plant is embedded. The
membrane of the cyst (perithecium) is usually
* L. R. Tulasne, Recherches sur les Uredinées
&c. Ann. des Sc. Nat. 3me. S. t. vii. p. 12.