The ascocarps are surrounded by a _complete envelope_ without any
opening: the fruit-bodies are cleistocarpic; the spores are only
liberated after the disintegration of the fruit-bodies. Paraphyses
are wanting. The two first orders have in addition the means of
reproduction by conidia.
Order 1. =Erysiphaceæ, Mildews.= The Fungi belonging to this order are
epiphytic parasites, whose mycelium, somewhat resembling a cobweb, may
be seen on the leaves and other green portions of plants (see Figs.
107, 108). The hyphæ ramify in all directions upon the surface of their
host, and emit haustoria which penetrate the epidermal cells, and
thus derive the necessary nutriment. The Mildew-Fungi thus belong to
the obligate parasites, and during their growth dwarf and destroy the
portions of their host on which they live. The reproduction takes place
in the first instance by abstriction of conidio-chains from the end of
special branches (Fig. 108 _c_, a hypha is seen in the act of detaching
a conidium). The conidia may germinate immediately, and thus quickly
reproduce their species. When present in large numbers they appear as
a white meal covering the surface of the plant on which the fungus is
found. Later on appear the dark brown, spheroid ascocarps (Fig. 108
_a_) which, although small, are generally just visible to the naked eye
as black specks.
[Illustration: FIG. 107.--_Erysiphe cichoracearum_: _a_
mycelium-threads; _b_ sterile hypha (“pollinodium”); _c_ fertile
hypha (ascogone or archicarp); _d_ and _e_ young ascocarps.]
A characteristic feature of the Mildew-Fungi is the thin,
pseudo-parenchymatous covering of the ascocarp, enclosing _one_
(_Podosphæra_ and _Sphærotheca_; compare _Thelebolus_ among the
Hemiasci) or _a few_ asci (Fig. 108 _c_), which do not form
any hymenium, but are irregularly placed. The cells of the
ascocarp-envelope are often prolonged into hair-like appendages.
The ascocarps are developed from the mycelium at places where two
hyphæ cross each other (Fig. 107). At these places two short and
erect hyphæ are produced side by side. The one from the lower hypha
(Fig. 107 _c_) assumes an ellipsoidal shape, and is known as the
_archicarp_ or _ascogone_, while the other (“_pollinodium_”) arches
over the ascogone. From the latter one ascus may be at once developed
(_Sphærotheca_, etc.), or after its division several asci may be
produced, each developed from one division. The sterile hypha (termed
“pollinodium,” since it was formerly, but erroneously, supposed to
fertilise the ascogone) produces a number of branches, and forms the
pseudo-parenchymatous envelope of one cell in thickness, enclosing the
asci.
[Illustration: FIG. 108.--_Erysiphe communis._ A small portion
of a leaf with this Fungus growing upon it (considerably
magnified). The hyphæ b and d do not belong to this Fungus, but
are reproductive organs of a pyrenomycetous Fungus parasitic upon
it (_Cicinnobolus_).]
Many plants, both cultivated and wild, are attacked by various species
of Mildew. A common means of prevention against their attacks is to
dust the diseased parts with sulphur.
[Illustration: FIG. 109.--_Eurotium glaucum_: α portion of
mycelium lying horizontally; β vertically-placed conidiophore;
the mycelium gives rise to another branch near α; the conidia are
abstricted from short flask-shaped cells; _b_ a ripe conidium;
_c_, _d_ germinating conidia; _e_ spirally-twisted hypha,
commencement of an ascocarp; _f_ a stage later; _g_ still later,
the hypha at the base of the coil has given off branches which
are applied to it; _h_, _i_ sections of young ascocarps.]
_Sphærotheca pannosa_ occurs on the leaves of Roses, and on the
fruit of Peaches and Apricots. _S. castagnei_ on _Humulus_,
_Cucumis_, etc.--_Erysiphe tuckeri_ grows on the leaves and
fruit of the Vine; it spins its hyphæ over the bunches of
grapes, curtails their growth, and causes them to burst, and
to become decayed and rotten (Grape-disease). The Fungus was
first noticed in England in 1845, and later was found in
all countries where grapes are grown. It is only known in
the conidial form (“Oidium tuckeri”). Many other species of
_Erysiphe_ are found on herbaceous plants.--_Microsphæra_ has
appendages which are repeatedly forked at their extremities.
_M. grossulariæ_ on _Ribes grossularia_.--_Uncinula_ has
appendages with spirally-coiled extremities; on _Salix_ and
_Acer_.--_Phyllactinia_ has a circle of bristle-like appendages
with dilated bases. _P. guttata_ on _Corylus_, _Fraxinus_,
_Fagus_, etc.
Order 2. =Perisporiaceæ=, Moulds and Mildews. A group of Fungi
widely distributed and found in all situations. Usually they have a
well-developed surface mycelium, and small, round, seldom conspicuous
ascocarps, containing ovoid, pulley-like spores. They are partly
saprophytic, partly parasitic, in the latter condition having a brown
mycelium.
[Illustration: FIG. 110.--_Eurotium glaucum_: _a_ longitudinal
section of a half-ripe ascocarp, bounded externally by a
well-defined layer of cells, enclosing asci in various stages of
development; _b_ a semi-ripe, _c_ an almost ripe ascus; _d_ and
_e_ spores seen from the edge and side; _f_ germinating spore
twenty-two hours after been sown in plum juice.]
_Eurotium glaucum_ (= _E. herbariorum_, Figs. 109, 110) and _E. repens_
live on dead organic matter, preserved fruits, etc. The conidial forms
of both species are known as “Moulds” (Fig. 109), and formerly were
described under the name “_Aspergillus glaucus_.” The conidia for some
time remain attached to each other in chains (Fig. 109 _a_); they are
abstricted from sterigmata arranged radially on the spherical, swollen
end of the conidiophore. The small yellow or brownish ascocarps are
frequently found in herbaria, especially when the specimens have
been insufficiently dried. _Aspergillus fumigatus_ and others are
pathogenic, causing mycosis in warm-blooded animals.
[Illustration: FIG. 111.--_Penicillium crustaceum_: _a_ conidia
(× 300); _b_ germination of conidia; _c_ small portion of
mycelium, produced from a conidium at *, with five conidiophores;
_d_ young conidiophore (× 630), a flask-shaped cell is
abstricting a conidium; _e_ the same conidiophore after 9–10
hours.]
[Illustration: FIG. 112.--_Penicillium crustaceum_: _a_ two
spirally-coiled hyphæ arise from the mycelium, from one of
which (archicarp) the asci are produced; _b_ a further step in
the development of the ascocarp; the branching archicarp is
surrounded by sterile hyphæ; _c_ section of young ascocarp;
the larger hyphæ in the centre are the ascogenous hyphæ; these
are enclosed by a pseudo-parenchyma of sterile hyphæ (× 300);
_d_ series of ripe asci with spores; _e_ four ascopores seen
laterally; _f_ germinating ascospores (× 800).]
_Penicillium crustaceum_ (_P. glaucum_, Figs. 111, 112) is an
exceedingly common “Mould.” Its mycelium appears very frequently on
any organic matter which is permitted to remain untouched, and soon
covers it with a dense mass of blue-green conidiophores. These branch
at their summits and bear flask-shaped cells from which the conidia
are abstricted. The ascocarps which, both in size and colour, resemble
grains of sand, have only been obtained in luxuriant cultivation with a
limited supply of oxygen.
_Capnodium salicinum_ (_Fumago salicina_, _Cladosporium
fumago_), a common Mildew, forms dark overgrowths on the leaves
and branches of various shrubs (Poplars, Elms, Willows) and on
Hops. The conidia appear in various forms, as on conidiophores,
in conidiocarps with large multicellular conidia, and in
conidiocarps with small unicellular conidia; in nutritive
solutions yeast-like conidia are also developed.--_Apiosporium
pinophilum_ produces mildew on the leaves of _Abies alba_ and
_Picea excelsa_. (The conidial-forms were formerly described as
“_Antennaria pinophila_”).
Order 3. =Tuberaceæ, Truffles.= The Fungi belonging to this order
are entirely subterranean. The mycelium is filamentous, and partly
parasitic upon the roots of plants, especially trees, in its
neighbourhood; it is then known as _Mycorhiza_. The fruit-body is
relatively large, in some cases about the size of a hen’s egg.
Internally it is traversed by a number of winding passages (Fig. 113
_a_), the walls of which are coated with the asci. The asci (_b_)
contain only a small number of spores, and these are set free by the
putrefaction of the fruit-body. Conidia are unknown.
[Illustration: FIG. 113.--_Tuber melanosporum_: _a_ fruit-body
(nat. size), a portion having been removed to show the internal
structure; _b_ an ascus with ascospores.]
_Tuber melanosporum_, _T. brumale_, _T. æstivum_, and other
species are edible. _Terfezia leonis_ and _Choiromyces
mæandriformis_ are also edible. The Truffles are always found in
woods and under trees, and disappear when these are destroyed.
France and Italy produce the best and the largest number of
Truffles, which are hunted by specially trained dogs and pigs.
In _Elaphomyces_ (Stag-Truffle) the fruit-body has a corky
external layer, and is inedible. Some of the species are found
in this country. _E. granulatus_ is parasitic on the roots of
the Fir.