given by De Bary in a paper from which we have already quoted.[D] He
writes thus:--In every household there is a frequent unbidden guest,
which appears particularly on preserved fruits, viz., the _mould_
which is called _Aspergillus glaucus_. It shows itself to the naked
eye as a woolly floccy crust over the substance, first purely white,
then gradually covered with little fine glaucous, or dark green dusty
heads. More minute microscopical examination shows that the fungus
consists of richly ramified fine filaments, which are partly
disseminated in the substratum, and partly raised obliquely over it.
They have a cylindrical form with rounded ends, and are divided into
long outstretched members, each of which possesses the property which
legitimatizes it as a vesicle in the ordinary sense of the word; it
contains, enclosed within a delicate structureless wall, those bodies
which bear the appearance of a finely granulated mucous substance,
which is designated by the name of protoplasm, and which either
equally fills the cells, or the older the cell the more it is filled
with watery cavities called vacuoles.
All parts are at first colourless. The increase in the length of the
filaments takes place through the preponderating growth near their
points; these continually push forward, and, at a short distance from
them, successive new partitions rise up, but at a greater distance,
the growth in the length ceases. This kind of growth is called point
growth. The twigs and branches spring up as lateral dilatations of
the principal filament, which, once designed, enlarges according to
the point growth. This point growth of every branch is, to a certain
extent, unlimited. The filaments in and on the substratum are the
first existing members of the fungus; they continue so long as it
vegetates. As the parts which absorb nourishment from and consume the
substance, they are called the _mycelium_. Nearly every fungus
possesses a mycelium, which, without regard to the specific difference
of form and size, especially shows the described nature in its
construction and growth.
The superficial threads of the mycelium produce other filaments beside
those numerous branches which have been described, and which are the
fruit thread (carpophore) or conidia thread. These are on an average
thicker than the mycelium threads, and only exceptionally ramified or
furnished with partitions; they rise almost perpendicularly into the
air, and attain a length of, on an average, half a millimetre, or
one-fiftieth of an inch, but they seldom become longer, and then their
growth is at an end. Their free upper end swells in a rounded manner,
and from this is produced, on the whole of its upper part, rayed
divergent protuberances, which attain an oval form, and a length
almost equal to their radius, or, in weaker specimens, the diameter of
the rounded head. The rayed divergent protuberances are the direct
producers and bearers of the propagating cells, spores, or conidia,
and are called sterigmata. Every sterigma at first produces at its
point a little round protuberance, which, with a strong narrow basis,
rests upon the sterigma. These are filled with protoplasm, swell more
and more, and, after some time, separate themselves by a partition
from the sterigma into independent cells, spores, or conidia.
The formation of the first spore takes place at the same end of the
sterigma, and in the same manner a second follows, then a third, and
so on; every one which springs up later pushes its predecessor in the
direction of the axis of the sterigma in the same degree in which it
grows itself; every successive spore formed from a sterigma remains
for a time in a row with one another. Consequently every sterigma
bears on its apex a chain of spores, which are so much the older, the
farther they stand from the sterigma. The number of the links in a
chain of spores reaches in normal specimens to ten or more. All
sterigmata spring up at the same time, and keep pace with one another
in the formation of the spores. Every spore grows for a time,
according to its construction, and at last separates itself from its
neighbours. The mass of dismembered spores forms that fine glaucous
hue which is mentioned above. The spores, therefore, are articulated
in rows, one after the other, from the ends of the sterigmata. The
ripe spore, or conidium, is a cell of a round or broadly oval form,
filled with a colourless protoplasm, and, if observed separately, is
found to be provided with a brownish, finely verruculose, dotted
wall.
[Illustration: FIG. 102.--_a._ _Aspergillus glaucus_; _b._ conidia; _c._
germinating conidium; _d._ conceptacle of _Eurotium_; _e._ ascus.]
The same mycelium which forms the pedicel for the conidia when it is
near the end of its development, forms by normal vegetation a second
kind of fructification. It begins as delicate thin little branches,
which are not to be distinguished by the naked eye, and which mostly
in four or six turns, after a quickly terminated growth, wind their
ends like a corkscrew. (Fig. 102.) The sinuations decrease in width
more and more, till they at last reach close to one another, and the
whole end changes from the form of a corkscrew into that of a hollow
screw. In and on that screw-like body, a change of a complicated kind
takes place, which is a productive process. In consequence of this,
from the screw body a globose receptacle is formed, consisting of a
thin wall of delicate cells, and a closely entwined row of cells
surrounded by this dense mass (_d_). By the enlargement of all these
parts the round body grows so much, that by the time it is ripe it is
visible to the naked eye. The outer surface of the wall assumes a
compactness and a bright yellow colour; the greater part of the cells
of the inner mass become asci for the formation of sporidia, while
they free themselves from the reciprocal union, take a broad oval
form, and each one produces within its inner space eight sporidia
(_e_). These soon entirely fill the ascus. When they are quite ripe,
the wall of the conceptacle becomes brittle, and from irregular
fissures, arising easily from contact, the colourless round sporidia
are liberated.
The pedicels of both kinds of fruit are formed from the same mycelium
in the order just described. If we examine attentively, we can often
see both springing up close to one another from the same filament of a
mycelium. This is not very easy in the close interlacing of the stalks
of a mass of fungi in consequence of their delicacy and fragility.
Before their connection was known, the conceptacles and the conidia
pedicels were considered as organs of two very different species of
fungi. The conceptacles were called _Eurotium herbariorum_, and the
conidia bearers were called _Aspergillus glaucus_.
Allied to _Eurotium_ is the group of _Erysiphei_, in which
well-authenticated polymorphy prevails. These fungi are developed
on the green parts of growing plants, and at first consist of a
white mouldy stratum, composed of delicate mycelium, on which erect
threads are produced, which break up into subglobose joints or
conidia. The species on grass was named _Oidium monilioides_
before its relationship was known, but undoubtedly this is only the
conidia of _Erysiphe graminis_. In like manner the vine disease
(_Oidium Tuckeri_) is most probably only the conidia of a species of
_Erysiphe_, of which the perfect condition has not yet been
discovered. On roses the old _Oidium leucoconium_ is but the conidia
of _Sphærotheca pannosa_, and so of other species. The _Erysiphe_
which ultimately appears on the same mycelium consists of globose
perithecia, externally furnished with thread-like appendages, and
internally with asci containing sporidia. In this genus there are
no less than five different forms of fruit,[E] the multiform
threads on the mycelium, already alluded to as forms of _Oidium_, the
asci contained in the sporangia, which is the proper fruit of the
_Erysiphe_, larger stylospores which are produced in other
sporangia, the smaller stylospores which are generated in the
pycnidia, and separate sporules which are sometimes formed in the
joints of the necklaces of the conidia. These forms are figured in the
"Introduction to Cryptogamic Botany" from _Sphærotheca Castagnei_,
which is the hop mildew.[F] The vine disease, hop mildew, and rose
mildew, are the most destructive species of this group, and the
constant annoyance of cultivators.
[Illustration: FIG. 103.--_Erysiphe cichoracearum._ _a._ Receptacle; _o._
mycelium. (De Bary.)]
When first describing an allied fungus found on old paper, and named
_Ascotricha chartarum_, the Rev. M. J. Berkeley called attention to
the presence of globose conidia attached to the threads which surround
the conceptacles,[G] and this occurred as long since as 1838. In a
recent species of _Chætomium_ found on old sacking, _Chætomium
griseum_, Cooke,[H] we have found tufts in all respects similar
externally to the _Chætomium_, but no perithecium was formed, naked
conidia being developed apparently at the base of the coloured
threads. In _Chætomium funicolum_, Cooke, a black mould was also found
which may possibly prove to be its conidia, but at present there is no
direct evidence.
The brothers Tulasne have made us acquainted with a greater
number of instances amongst the _Sphæriacei_ in which multiple
organs of reproduction prevail. Very often old and decaying
individuals belonging to species of _Boletus_ will be found
filled, and their entire substance internally replaced, by the
threads and multitudinous spores of a golden yellow parasite, to
which the name of _Sepedonium chrysospermum_ has been given.
According to Tulasne, this is merely a condition of a sphæriaceous
fungus belonging to his genus _Hypomyces_.[I]
The same observers also first demonstrated that _Trichoderma viride_,
P., was but the conidia-bearing stage of _Hypocrea rufa_, P., another
sphæriaceous fungus. The ascigerous stroma of the latter is indeed
frequently associated in a very close manner with the cushions of the
pretended _Trichoderma_, or in other cases the same stroma will give
rise to a different apparatus of conidia, of which the principal
elements are acicular filaments, which are short, upright, and almost
simple, and which give rise to small oval conidia which are solitary
on the tips of the threads. Therefore this _Hypocrea_ will possess two
different kinds of conidia, as is the case in many species of
_Hypomyces_.
A most familiar instance of dualism will be found in _Nectria
cinnabarina_, of which the conidia form is one of the most common of
fungi, forming little reddish nodules on all kinds of dead twigs.[J]
[Illustration: FIG. 104.--Twig with _Tubercularia_ on the upper portion,
_Nectria_ on the lower.]
Almost any small currant twig which has been lying on the ground in a
damp situation will afford an opportunity of studying this phenomenon.
The whole surface of the twig will be covered from end to end with
little bright pink prominences, bursting through the bark at regular
distances, scarcely a quarter of an inch apart. Towards one end of the
twig probably the prominences will be of a deeper, richer colour, like
powdered cinnabar. The naked eye is sufficient to detect some
difference between the two kinds of pustules, and where the two merge
into each other specks of cinnabar will be visible on the pink
projections. By removing the bark it will be seen that the pink bodies
have a sort of paler stem, which spreads above into a somewhat globose
head, covered with a delicate mealy bloom. At the base it penetrates
to the inner bark, and from it the threads of mycelium branch in all
directions, confined, however, to the bark, and not entering the woody
tissues beneath. The head, placed under examination, will be found to
consist of delicate parallel threads compacted together to form the
stem and head. Some of these threads are simple, others are branched,
bearing here and there upon them delicate little bodies, which are
readily detached, and which form the mealy bloom which covers the
surface. These are the conidia, little slender cylindrical bodies,
rounded at the ends.
[Illustration: FIG. 105.--Section of _Tubercularia_. _c._ Threads with
conidia.[K]]
Passing to the other bodies, which are of a deeper colour, it will
soon be discovered that, instead of being simple rounded heads, each
tubercle is composed of numerous smaller, nearly globose bodies,
closely packed together, often compressed, all united to a base
closely resembling the base of the other tubercles. If for a moment we
look at one of the tubercles near the spot where the crimson
tubercles seem to merge into the pink, we shall not only find them
particoloured, but that the red points are the identical globose
little heads just observed in clusters. This will lead to the
suspicion, which can afterwards be verified, that the red heads
are really produced on the stem or stroma of the pink tubercles.
A section of one of the red tubercles will show us how much the
internal structure differs. The little subglobose bodies which spring
from a common stroma or stem are hollow shells or capsules, externally
granular, internally filled with a gelatinous nucleus. They are,
indeed, the perithecia of a sphæriaceous fungus of the genus
_Nectria_, and the gelatinous nucleus contains the fructification.
Still further examination will show that this fructification consists
of cylindrical asci, each enclosing eight elliptical sporidia, closely
packed together, and mixed with slender threads called paraphyses.
Here, then, we have undoubted evidence of _Nectria cinnabarina_, with
its fruit, produced in asci growing from the stroma or stem, and in
intimate relationship with what was formerly named _Tubercularia
vulgaris_. A fungus with two forms of fruit, one proper to the pink,
or _Tubercularia_ form, with naked slender conidia, the other proper
to the mature fungus, enclosed in asci, and generated within the walls
of a perithecium. Instances of this kind are now known to be far from
uncommon, although they cannot always, or often, be so clearly and
distinctly traced as in the illustration which we have selected.
[Illustration: FIG. 106.--D. _Nectria_ surrounding _Tubercularia_; E.
tuft of _Nectria cinnabarina_; F. section of stroma; G. ascus and
paraphyses.]
It is not uncommon for the conidia of the _Sphæria_ to partake of the
characteristics of a mould, and then the perithecia are developed
amongst the conidial threads. A recently recorded instance of this
relates to _Sphæria Epochnii_, B. and Br.,[L] the conidia form of
which was long known before the _Sphæria_ related to it was
discovered, under the name of _Epochnium fungorum_. The _Epochnium_
forms a thin stratum, which overruns various species of _Corticium_.
The conidia are at first uniseptate. The perithecia of the _Sphæria_
are at first pale bottle-green, crowded in the centre of the
_Epochnium_, then black green granulated, sometimes depressed at the
summit, with a minute pore. The sporidia are strongly constricted in
the centre, at first uniseptate, with two nuclei in each division.
Another _Sphæria_ in which the association is undoubted is the
_Sphæria aquila_, Fr.,[M] which is almost always found nestling in a
woolly brown subiculum, for the most part composed of barren brown
jointed threads. These threads, however, produce, under favourable
conditions, mostly before the perfection of the perithecia, minute
subglobose conidia, and in this state constitute what formerly bore
the name of _Sporotrichum fuscum_, Link., but now recognized as the
conidia of _Sphæria aquila_.
In _Sphæria nidulans_, Schw., a North American species, we have more
than once found the dark brown subiculum bearing large triseptate
conidia, having all the characters of the genus _Helminthosporium_. In
_Sphæria pilosa_, P., Messrs. Berkeley and Broome have observed oblong
conidia, rather irregular in outline, terminating the hairs of the
perithecium.[N] The same authors have also figured the curious
pentagonal conidia springing from flexuous threads accompanying
_Sphæria felina_, Fckl.,[O] and also the threads resembling those of a
_Cladotrichum_ with the angular conidia of _Sphæria cupulifera_, B.
and Br.[P] A most remarkable example is also given by the Brothers
Tulasne in _Pleospora polytricha_, in which the conidia-bearing
threads not only surround, but grow upon the perithecia, and are
crowned by fascicles of septate conidia.[Q]
Instances of this kind have now become so numerous that only a few can
be cited as examples of the rest. It is not at all improbable that the
majority of what are now classed together as species under the genus
of black moulds, _Helminthosporium_, will at some not very distant
period be traced as the conidia of different species of ascomycetous
fungi. The same fate may also await other allied genera, but until
this association is established, they must keep the rank and position
which has been assigned to them.
Another form of dualism, differing somewhat in character from the
foregoing, finds illustration in the sphæriaceous genus _Melanconis_,
of Tulasne, in which the free spores are still called conidia, though
in most instances produced in a sort of spurious conceptaculum, or
borne on short threads from a kind of cushion-shaped stroma. In the
_Melanconis stilbostoma_,[R] there are three forms, one of slender
minute bodies, oozing out in the form of yellow tendrils, which may be
spermatia, formerly called _Nemaspora crocea_. Then there are the oval
brown or olive brown conidia, which are at first covered, then oozing
out in a black pasty mass, formerly _Melanconium bicolor_, and finally
the sporidia in asci of _Sphæria stilbostoma_, Fries. In _Melanconis
Berkeleii_, Tul., the conidia are quadrilocular, previously known as
_Stilbospora macrosperma_, B. and Br. In a closely-allied species from
North America, _Melanconis bicornis_, Cooke, the appendiculate
sporidia are similar, and the conidia would also appear to partake of
the character of _Stilbospora_. We may remark here that we have seen a
brown mould, probably an undescribed species of _Dematiei_, growing in
definite patches around the openings in birch bark caused by the
crumpent ostiola of the perithecia of _Melanconis stilbostoma_, from
the United States.
In _Melanconis lanciformis_,[S] Tul., there are, it would appear,
four forms of fruit. One of these consists of conidia, characterized
by Corda as _Coryneum disciforme_.[T] Stylospores, which are also
figured by Corda under the name of _Coniothecium betulinum_;
pycnidia,[U] first discovered by Berkeley and Broome, and named by
them _Hendersonia polycystis_;[V] and the ascophorous fruits which
constituted the _Sphæria lanciformis_ of Fries. Mr. Currey indicated
_Hendersonia polycystis_, B. and Br., as a form of fruit of this
species in a communication to the Royal Society in 1857.[W] He says
this plant grows upon birch, and is in perfection in very moist
weather, when it may be recognized by the large black soft
gelatinous protuberances on the bark, formed by spores escaping and
depositing themselves upon and about the apex of the perithecium.
This I suspect to be an abnormal state of a well-known Sphæria (_S.
lanciformis_), which grows upon birch, and upon birch only.
We might multiply, almost indefinitely, instances amongst the
_Sphæriacei_, but have already given sufficient for illustration, and
will therefore proceed briefly to notice some instances amongst the
_Discomycetes_, which also bear their complete or perfect fruit in
asci.
The beautiful purple stipitate cups of _Bulgaria sarcoides_, which may
be seen flourishing in the autumn on old rotten wood, are often
accompanied by club-shaped bodies of the same colour; or earlier in
the season these clavate bodies may be found alone, and at one time
bore the name of _Tremella sarcoides_. The upper part of these clubs
disseminate a great abundance of straight and very slender spermatia.
Earlier than this they are covered with globose conidia. The
fully-matured _Bulgaria_ develops on its hymenium clavate delicate
asci, each enclosing eight elongated hyaline sporidia, so that we have
three forms of fruit belonging to the same fungus, viz. conidia and
spermatia in the _Tremella_ stage, and sporidia contained in asci in
the mature condition.[X] The same phenomena occur with _Bulgaria
purpurea_, a larger species with different fruit, long confounded with
_Bulgaria sarcoides_.
On the dead stems of nettles it is very common to meet with small
orange tubercles, not much larger than a pin's head, which yield at
this stage a profusion of slender linear bodies, produced on delicate
branched threads, and at one time bore the name of _Dacrymyces
Urticæ_, but which are now acknowledged to be only a condition of a
little tremelloid _Peziza_ of the same size and colour, which might be
mistaken for it, if not examined with the microscope, but in which
there are distinct asci and sporidia. Both forms together are now
regarded as the same fungus, under the name of _Peziza fusarioides_,
B.
The other series of phenomena grouped together under the name of
polymorphism relate to forms which are removed from each other, so
that the mycelium is not identical, or, more usually, produced on
different plants. The first instance of this kind to which we shall
make reference is one of particular interest, as illustrative of the
old popular creed, that berberry bushes near corn-fields produced
mildewed corn. There is a village in Norfolk, not far from Great
Yarmouth, called "Mildew Rollesby," because of its unenviable
notoriety in days past for mildewed corn, produced, it was said, by
the berberry bushes, which were cut down, and then mildew disappeared
from the corn-fields, so that Rollesby no longer merited its
_sobriquet_. It has already been shown that the corn-mildew (_Puccinia
graminis_) is dimorphous, having a one-celled fruit (_Trichobasis_),
as well as a two-celled fruit (_Puccinia_). The fungus which attacks
the berberry is a species of cluster-cup (_Æcidium berberidis_), in
which little cup-like peridia, containing bright orange pseudospores,
are produced in tufts or clusters on the green leaves, together with
their spermogonia.