The perithecia are _pale, fleshy, brightly coloured_, and generally
aggregated on a stroma. Conidia and chlamydospores occur very
frequently. Only one order.
Order. =Hypocreaceæ.= In this order the majority are parasites upon
Flowering-plants (_Nectria_, _Polystigma_, _Epichloë_, _Claviceps_);
but some are parasites upon Fungi (_Hypomyces_, _Melanospora_), or upon
insects (_Cordyceps_).
[Illustration: FIG. 116.--_Claviceps purpurea. A_ Sclerotium
with stromata (_cl_) (× by 2). _B_ Stroma divided longitudinally
to show the perithecia (_cp_). _C_ A perithecium with the
surrounding hyphæ (_hy_). _D_ An ascus ruptured, with the eight
filamentous ascospores emerging.]
The most important member of this order is the ERGOT (_Claviceps
purpurea_, Figs. 114, 115, 116). This Fungus is found in the flowers of
many species of Grasses, especially the Rye, attacking and destroying
the ovaries. In the FIRST or CONIDIAL STAGE of the attack, the ovaries
are found covered with a white, irregularly folded mycelium (Fig. 114
_m_, Fig. 115), formed of numerous hyphæ woven together and penetrating
the wall of the ovary. From these a number of hyphæ (Fig. 114 _a_)
project into the air and abstrict from their apices the conidia (_b_)
which serve as reproductive organs. The mycelium also secretes a
sticky, stinking fluid (honey-dew) in which the conidia are embedded
in great numbers. The honey-dew exudes from the bases of the glumes,
and is greedily sought by flies, which thus carry the conidia to
other ovaries. In this manner fresh ears are infected, which might
escape were the conidia only distributed by the wind. This stage
formerly was regarded as an independent Fungus, known as _Sphacelia
segetum_ (Fig. 115). On germination, the conidia produce either a new
mycelium (Fig. 114 _d_, _c_), or new conidia. The SECOND or SCLEROTIUM
STAGE is the one in which the Fungus passes the winter. The mycelium
penetrates deeper and deeper into the attacked ovaries, their tissues
are destroyed and replaced by the hyphæ, which gradually become more
and more felted together. A firm, pseudo-parenchymatous mass of hyphæ
is thus formed at the base of the loosely-woven _Sphacelia_, which is
in part transformed into the hard sclerotium, and the remainder thrown
off. A dark, hard, poisonous body, longer than the natural grain,
is thus formed; these bodies are known as Ergots, and were formerly
considered to be a distinct species,--_Sclerotium clavus_ (“Secale
cornutum,” Ergot, Fig. 116 _A_, _c_). The THIRD STAGE, described as
_Claviceps purpurea_, is developed in the following spring from the
germinating sclerotium, which produces dark-red stromata with short
stalks. In the stroma numerous perithecia with asci and ascospores are
produced. The latter may infect young flowers of the cereals, in which
the disease is then developed as before.
[Illustration: FIG. 117.--_Nectria cinnabarina_: _a_ branch of
_Acer pseudoplatanus_, with conidial-layers and perithecia (nat.
size); _b_ a conidial-layer (_Tuberculoria vulgaris_); _c_, a
mass of perithecia. (_b_ and _c_ × 8.)]
Several species of the genus _Nectria_, with blood-red
perithecia, are found as dangerous parasites, especially _N.
ditissima_, which causes “Canker” in the Beech, Ash, and Apple,
etc.; _N. cucurbitula_, which appears on Pine-trees, and _N.
cinnabarina_ (Fig. 117), whose conidial form was formerly named
_Tubercularia vulgaris_.--_Polystigma rubrum_ forms shining
red spots on the green leaves of _Prunus_-species.--_Epichloë
typhina_ is parasitic on the sheaths of Grasses, on which it
first forms a white conidial-layer, later on a yellow layer of
perithecia.--_Cordyceps_ (Chrysalis Fungus, Figs. 118, 119)
lives in and destroys insects, and after compassing their death
produces the club-formed, generally yellow, stromata, one part
of which bears conidia (_Isaria_) and another perithecia. _C.
militaris_ (Fig. 118) on the chrysalides and caterpillars of
moths, is the most common.
The so-called _Botrytis bassiana_, which produces the disease
known by the name of “Muscardine,” in silkworms, is probably a
conidial form belonging to _Cordyceps_.
[Illustration: FIG. 118.--_Cordyceps militaris._ I Stromata with
conidiophores (_Isaria farinosa_). II A larva, with stromata,
bearing perithecia. III A spore.]
[Illustration: FIG. 119.--_Cordyceps robertii_ on the larva of
_Hepialus virescens_: _a_ stalk of stroma; _b_ perithecia.]