Bary, seemed disposed to exclude this group from the vegetable kingdom
altogether, and relegate them to a companionship with amoeboid forms.
But in more recent works he seems to have reconsidered, and almost, if
not entirely, abandoned, that disposition. These fungi, mostly minute,
are characterized in their early stages by their gelatinous nature.
The substance of which they are then composed bears considerable
resemblance to sarcode, and, did they never change from this, there
might be some excuse for doubting as to their vegetable nature; but as
the species proceed towards maturity they lose their mucilaginous
texture, and become a mass of spores, intermixed with threads,
surrounded by a cellular peridium. Take, for instance, the genus
_Trichia_, and we have in the matured specimens a somewhat globose
peridium, not larger than a mustard seed, and sometimes nearly of the
same colour; this ultimately ruptures and exposes a mass of minute
yellow spherical spores, intermixed with threads of the same
colour.[V] These threads, when highly magnified, exhibit in themselves
a spiral arrangement, which has been the basis of some controversy,
and in some species these threads are externally spinulose. The chief
controversy on these threads has been whether the spiral markings are
external or internal, whether caused by twisting of the thread or by
the presence of an external or internal fibre. The spiral appearance
has never been called in question, only the structure from whence it
arises, and this, like the striæ of diatoms, is very much an open
question. Mr. Currey held that the spiral appearance may be accounted
for by supposing the existence of an accurate elevation in the wall of
the cell, following a spiral direction from one end of the thread to
the other. This supposition would, he thinks, accord well with the
optical appearances, and it would account exactly for the undulations
of outline to which he alludes. He states that he had in his
possession a thread of _Trichia chrysosperma_, in which the spiral
appearance was so manifestly caused by an elevation of this nature, in
which it is so clear that no internal spiral fibre exists, that he did
not think there could be a doubt in the mind of any person carefully
examining it with a power of 500 diameters that the cause of the
spiral appearance was not a spiral fibre. In _Arcyria_, threads of a
different kind are present; they mostly branch and anastomose, and are
externally furnished with prominent warts or spines, which Mr.
Currey[W] holds are also arranged in a spiral manner around the
threads. In other Myxogastres, threads are also present without any
appreciable spiral markings or spines. In the mature condition of
these fungi, they so clearly resemble, and have such close affinities
with, the Trichogastres that one is led almost to doubt whether it was
not on hasty grounds, without due examination or consideration, that
proposals were made to remove them from the society of their kindred.
[Illustration: FIG. 11.--_Arcyria incarnata_, with portion of threads and
spore, magnified.]
Very little is known of the development of the spores in this group;
in the early stages the whole substance is so pulpy, and in the latter
so dusty, whilst the transition from one to the other is so rapid,
that the relation between the spores and threads, and their mode of
attachment, has never been definitely made out. It has been supposed
that the spinulose projections from the capillitium in some species
are the remains of pedicels from which, the spores have fallen, but
there is no evidence beyond this supposition in its favour, whilst on
the other hand, in _Stemonitis_, for instance, there is a profuse
interlacing capillitium, and no spines have been detected. In order to
strengthen the supposition, spines should be more commonly present.
The threads, or capillitium, form a beautiful reticulated network in
_Stemonitis_, _Cribraria_, _Diachæa_, _Dictydium_, &c. In _Spumaria_,
_Reticularia_, _Lycogala_, &c., they are almost obsolete.[X] In no
group is the examination of the development of structure more
difficult, for the reasons already alleged, than in the Myxogastres.
[Illustration: FIG. 12.--_Diachæa elegans._]
[Illustration: FIG. 13.--_Cyathus vernicosus._]
NIDULARIACEI.--This small group departs in some important particulars
from the general type of structure present in the rest of the
Gasteromycetes.[Y] The plants here included may be described under
three parts, the mycelium, the peridium, and the sporangia. The
mycelium is often plentiful, stout, rigid, interlacing, and coloured,
running over the surface of the soil, or amongst the vegetable débris
on which the fungi establish themselves. The peridia are seated upon
this mycelium, and in most instances are at length open above, taking
the form of cups, or beakers. These organs consist of three strata of
tissue varying in structure, the external being fibrous, and sometimes
hairy, the interior cellular and delicate, the intermediate thick and
at length tough, coriaceous, and resistant. When first formed, the
peridia are spherical, they then elongate and expand, the mouth being
for some time closed by a veil, or diaphragm, which ultimately
disappears. Within the cups lentil-shaped bodies are attached to the
base and sides by elastic cords. These are the sporangia. Each of
these has a complicated structure; externally there is a filamentous
tunic, composed of interlaced fibres, sometimes called the peridiole;
beneath this is the cortex, of compact homogenous structure, then
follows a cellular thicker stratum, bearing, towards the centre of the
sporangia, delicate branched threads, or sporophores, on which, at
their extremities, the ovate spores are generated, sometimes in pairs,
but normally, it would seem that they are quaternary on spicules, the
threads being true basidia. The whole structure is exceedingly
interesting and peculiar, and may be studied in detail in Tulasne's
memoir on this group.
SPHÆRONEMEI.--In this very large and, within certain limits, variable
order, there is but little of interest as regards structure, which is
not better illustrated elsewhere; as, for instance, some sort of
perithecium is always present, but this can be better studied in the
_Sphæriacei_. The spores are mostly very minute, borne on delicate
sporophores, which originate from the inner surface of the perithecia,
but the majority of so-called species are undoubtedly conditions of
sphæriaceous fungi, either spermatogonia or pycnidia, and are of much
more interest when studied in connection with the higher forms to
which they belong.[Z] Probably the number of complete and autonomous
species are very few.
[Illustration: FIG. 14.--_Cyathus._ _a._ Sporangium. _b._ Section. _c._
Sporophore. _d._ Spores.]
MELANCONIEI.--Here, again, are associated together a great number of
what formerly were considered good species of fungi, but which are
now known to be but conditions of other forms. One great point of
distinction between these and the preceding is the absence of any
true perithecium, the spores being produced in a kind of spurious
receptacle, or from a sort of stroma. The spores are, as a rule,
larger and much more attractive than in _Sphæronemei_, and, in
some instances, are either very fine, or very curious. Under this
head we may mention the multiseptate spores of _Coryneum_; the
tri-radiate spores of _Asterosporium_; the curious crested spores of
_Pestalozzia_; the doubly crested spores of _Dilophospora_; and the
scarcely less singular gelatinous coated spores of _Cheirospora_.
In all cases the fructification is abundant, and the spores frequently
ooze out in tendrils, or form a black mass above the spurious
receptacle from which they issue.[a]
[Illustration: FIG. 15.--_Asterosporium Hoffmanni._]
TORULACEI.--In this order there seems at first to be a considerable
resemblance to the _Dematiei_, except that the threads are almost
obsolete, and the plant is reduced to chains of spores, without trace
of perithecium, investing cuticle, or definite stroma. Sometimes the
spores are simple, in other cases septate, and in _Sporochisma_ are at
first produced in an investing cell. In most cases simple threads at
length become septate, and are ultimately differentiated into spores,
which separate at the joints when fully mature.
[Illustration: FIG. 16.--Barren Cysts and Pseudospores of _Lecythea_.]
[Illustration: FIG. 17.--_Coleosporium Tussilaginis_, Lev.]
[Illustration: FIG. 18.--_Melampsora salicina._]
CÆOMACEI.--Of far greater interest are the Coniomycetous parasites
on living plants. The present order includes those in which the
spore[b] is reduced to a single cell; and here we may observe that,
although many of them are now proved to be imperfect in themselves,
and only forms or conditions of other fungals, we shall write of them
here without regard to their duality. These originate, for the most
part, within the tissues of living plants, and are developed outwards
in pustules, which burst through the cuticle. The mycelium penetrates
the intercellular passages, and may sometimes be found in parts
of the plants where the fungus does not develop itself. There is no
proper excipulum or peridium, and the spores spring direct from a
more compacted portion of the mycelium, or from a cushion-like
stroma of small cells. In _Lecythea_, the sub-globose spores are at
first generated at the tips of short pedicels, from which they are
ultimately separated; surrounding these spores arise a series of
barren cells, or cysts, which are considerably larger the true spores,
and colourless, while the spores are of some shade of yellow or
orange.[c] In _Trichobasis_, the spores are of a similar character,
sub-globose, and at first pedicellate; but there are no surrounding
cysts, and the colour is more usually brown, although sometimes
yellow. In _Uredo_, the spores are at first generated singly, within
a mother cell; they are globose, and either yellow or brown, without
any pedicel. In _Coleosporium_, there are two kinds of spores,
those of a pulverulent nature, globose, which are sometimes produced
alone at the commencement of the season, and others which originate
as an elongated cell; this becomes septate, and ultimately separates
at the joints. During the greater part of the year, both kinds of
spores are to be found in the same pustule. In _Melampsora_, the
winter spores are elongated and wedge-shaped, compacted together
closely, and are only matured during winter on dead leaves; the summer
spores are pulverulent and globose, being, in fact, what were until
recently regarded as species of _Lecythea_. In _Cystopus_, the spores
are sub-globose, or somewhat angular, generated in a moniliform
manner, and afterwards separating at the joints. The upper spore is
always the oldest, continuous production of spores going on for some
time at the base of the chain. Under favourable conditions of
moisture, each of these spores, or conidia, as De Bary terms them, is
capable of producing within itself a number of zoospores;[d] these
ultimately burst the vesicle, move about by the aid of vibratile
cilia, and at last settle down to germinate. Besides these, other
reproductive bodies are generated upon the mycelium, within the
tissues of the plant, in the form of globose oogonia, or resting
spores, which, when mature, also enclose great numbers of zoospores.
Similar oogonia are produced amongst the _Mucedines_ in the genus
_Peronospora_, to which De Bary considers _Cystopus_ to be closely
allied. At all events, this is a peculiarity of structure and
development not as yet met with in any other of the _Cæomacei_. In
_Uromyces_ is the nearest approach to the _Pucciniæi_; in fact, it is
_Puccinia_ reduced to a single cell. The form of spore is usually
more angular and irregular than in _Trichobasis_, and the pedicel is
permanent. It may be remarked here, that of the foregoing genera,
many of the species are not autonomous that have hitherto been
included amongst them. This is especially true of _Lecythea_,
_Trichobasis_, and, as it now appears, of _Uromyces_.[e]
[Illustration: FIG. 19.--_Cystopus candidus._]
[Illustration: FIG. 20.--_Xenodochus carbonarius._]
[Illustration: FIG. 21.--_Phragmidium bulbosum._]
PUCCINIÆI.--This group differs from the foregoing chiefly in having
septate spores. The pustules, or sori, break through the cuticle in a
similar manner, and here also no true peridium is present. In
_Xenodochus_, the highest development of joints is reached, each
spore being composed of an indefinite number, from ten to twenty
cells. With it is associated an unicellular yellow Uredine, of which
it is a condition. Probably, in every species of the _Pucciniæi_, it
may hereafter be proved, as it is now suspected, that an unicellular
Uredine precedes or is associated with it, forming a condition, or
secondary form of fruit of that species. Many instances of that kind
have already been traced by De Bary,[f] Tulasne, and others, and some
have been a little too rashly surmised by their followers. In
_Phragmidium_, the pedicel is much more elongated than in _Xenodochus_,
and the spore is shorter, with fewer and a more definite number of
cells for each species; Mr. Currey is of opinion that each cell of
the spore in _Phragmidium_ has an inner globose cell, which he caused
to escape by rupture of the outer cell wall as a sphæroid nucleus,[g]
leading to the inference that each cell has its own individual power
of germination and reproduction. In _Triphragmium_, there are three
cells for each spore, two being placed side by side, and one
superimposed. In one species, however, _Triphragmium deglubens_
(North American), the cells are arranged as in _Phragmidium_, so that
this represents really a tricellular _Phragmidium_, linking the present
with the latter genus. In _Puccinia_ the number of species is by far the
most numerous; in this genus the spores are uniseptate, and, as in
all the _Pucciniæi_, the peduncles are permanent. There is great
variability in the compactness of the spores in the sori, or pulvinules.
In some species, the sori are so pulverulent that the spores are as
readily dispersed as in the Uredines, in others they are so compact as
to be separated from each other with great difficulty. As might be
anticipated, this has considerable effect on the contour of the spores,
which in pulverulent species are shorter, broader, and more ovate than
in the compact species. If a section of one of the more compact sori be
made, it will be seen that the majority of the spores are side by side,
nearly at the same level, their apices forming the external surface
of the sori, but it will not be unusual to observe smaller and
younger spores pushing up from the hymenial cells, between the
peduncles of the elder spores, leading to the inference that there is a
succession of spores produced in the same pulvinule. In _Podisoma_, a
rather anomalous genus, the septate spores are immersed in a
gelatinous stratum, and some authors have imagined that they have an
affinity with the Tremellini, but this affinity is more apparent than
real. The phenomena of germination, and their relations to _Roestelia_,
if substantiated, establish their claim to a position amongst the
_Pucciniæi_.[h] It seems to us that _Gymnosporangium_ does not differ
generically from _Podisoma_. In a recently-characterized species,
_Podisoma Ellisii_, the spores are bi-triseptate. This is, moreover,
peculiar from the great deficiency in the gelatinous element. In
another North American species, called _Gymnosporangium biseptatum_,
Ellis, which is distinctly gelatinous, there are similar biseptate
spores, but they are considerably broader and more obtuse. In other
described species they are uniseptate.
[Illustration: FIG. 22.--Pseudospores of _Puccinia_.]
USTILAGINEI.--These fungi are now usually treated as distinct from the
_Cæomacei_, to which they are closely related.[i] They are also
parasitic on growing plants, but the spores are usually black or
sooty, and never yellow or orange; on an average much smaller than in
the _Cæomacei_. In _Tilletia_, the spores are spherical and
reticulated, mixed with delicate threads, from whence they spring. In
the best known species, _Tilletia caries_, they constitute the "bunt"
of wheat. The peculiarities of germination will be alluded to
hereafter. In _Ustilago_, the minute sooty spores are developed either
on delicate threads or in compacted cells, arising first from a sort
of semi-gelatinous, grumous stroma. It is very difficult to detect any
threads associated with the spores. The species attack the flowers and
anthers of composite and polygonaceous plants, the leaves, culms, and
germen of grasses, &c., and are popularly known as "smuts." In
_Urocystis_ and _Thecaphora_, the spores are united together into
sub-globose bodies, forming a kind of compound spore. In some species
of _Urocystis_, the union which subsists between them is comparatively
slight. In _Thecaphora_, on the contrary, the complex spore, or
agglomeration of spores, is compact, being at first apparently
enclosed in a delicate cyst. In _Tuburcinia_, the minute cells are
compacted into a hollow sphere, having lacunæ communicating with the
interior, and often exhibiting the remains of a pedicel.
[Illustration: FIG. 23.--_Thecaphora hyalina._]
[Illustration: FIG. 24.--_Æcidium Berberidis._]
ÆCIDIACEI.--This group differs from the foregoing three groups
prominently in the presence of a cellular peridium, which encloses
the spores; hence some mycologists have not hesitated to propose
their association with the Gasteromycetes, although every other
feature in their structure seems to indicate a close affinity
with the _Cæomacei_. The pretty cups in the genus _Æcidium_ are
sometimes scattered and sometimes collected in clusters, either with
spermogonia in the centre or on the opposite surface. The cups
are usually white, composed of regularly arranged bordered cells
at length bursting at the apex, with the margins turned back and
split into radiating teeth. The spores are commonly of a bright
orange or golden yellow, sometimes white or brownish, and are
produced in chains, or moniliform strings, slightly attached to
each other,[j] and breaking off at the summit at the same time that
they continue to be produced at the base, so that for some time
there is a successive production of spores. The spermogonia are
not always readily detected, as they are much smaller than the
peridia, and sometimes precede them. The spermatia are expelled
from the lacerated and fringed apices, and are very minute and
colourless. In _Roestelia_ the peridia are large, growing in
company, and splitting longitudinally in many cases, or by a
lacerated mouth. In most instances, the spores are brownish, but
in a splendid species from North America (_Roestelia aurantiaca_,
Peck), recently characterized, they are of a bright orange. If
Oersted is correct in his observations, which await confirmation,
these species are all related to species of _Podisoma_ as a
secondary form of fruit.[k] In the _Roestelia_ of the pear-tree, as
well as in that of the mountain ash, the spermogonia will be found
either in separate tufts on discoloured spots, or associated with
the _Roestelia_, In _Peridermium_ there is very little structural
difference from _Roestelia_, and the species are all found on
coniferous trees. In _Endophyllum_, the peridia are immersed in the
succulent substance of the matrix; whilst in _Graphiola_, there is
a tougher and withal double peridium, the inner of which forms a
tuft of erect threads resembling a small brush.[l]
[Illustration: FIG. 25.--_Helminthosporium molle._]
HYPHOMYCETES.--The predominant feature in the structure of this order
has already been intimated to consist in the development of the
vegetative system under the form of simple or branched threads, on
which the fruit is generated. The common name of mould is applied to
them perhaps more generally than to other groups, although the term is
too vague, and has been too vaguely applied to be of much service in
giving an idea of the characteristics of this order. Leaving the
smaller groups, and confining ourselves to the _Dematiei_ and the
_Mucedines_, we shall obtain some notion of the prevalent structure.
In the former the threads are more or less carbonized, in the latter
nearly colourless. One of the largest genera in _Dematiei_ is
_Helminthosporium_. It appears on decaying herbaceous plants, and on
old wood, forming effused black velvety patches. The mycelium, of
coloured jointed threads, overlays and penetrates the matrix; from
this arise erect, rigid, and usually jointed threads, of a dark brown,
nearly black colour at the base, but paler towards the apex. In most
cases these threads have an externally cortical layer, which imparts
rigidity; usually from the apex, but sometimes laterally, the spores
are produced. Although sometimes colourless, these are most commonly
of some shade of brown, more or less elongated, and divided
transversely by few or many septa. In _Helminthosporium Smithii_, the
spores much exceed the dimensions of the threads;[m] in other species
they are smaller. In _Dendryphium_, the threads and spores are very
similar, except that the threads are branched at their apex, and the
spores are often produced one at the end of another in a short
chain.[n] In _Septosporium_ again, the threads and spores are similar,
but the spores are pedicellate, and attached at or near the base;
whilst in _Acrothecium_, with similar threads and spores, the latter
are clustered together at the apex of the threads. In _Triposporium_,
the threads are similar, but the spores are tri-radiate; and in
_Helicoma_, the spores are twisted spirally. Thus, we might pass
through all the genera to illustrate this chief feature of coloured,
septate, rather rigid, and mostly erect threads, bearing at some point
spores, which in most instances are elongated, coloured, and septate.
[Illustration: FIG. 26.--_Acrothecium simplex._]
[Illustration: FIG. 27.--_Peronospora Arenariæ._]