mushroom belongs, an examination of that species will be almost
sufficient. Here we shall at once recognize three distinct parts
requiring elucidation, viz. the rooting slender fibres that traverse
the soil, and termed the _mycelium_, or spawn, the stem and cap or
pileus, which together constitute what is called the _hymenophore_,
and the plates or gills on the under surface of the cap, which bear
the _hymenium_. The earliest condition in which the mushroom can be
recognized as a vegetable entity is in that of the "spawn" or
mycelium, which is essentially an agglomeration of vegetating spores.
Its normal form is that of branched, slender, entangled, anastomosing,
hyaline threads. At certain privileged points of the mycelium, the
threads seem to be aggregated, and become centres of vertical
extension. At first only a small nearly globose budding, like a grain
of mustard seed, is visible, but this afterwards increases rapidly,
and other similar buddings or swellings appear at the base.[A] These
are the young hymenophore. As it pushes through the soil, it
gradually loses its globose form, becomes more or less elongated, and
in this condition a longitudinal section shows the position of the
future gills in a pair of opposite crescent-shaped darker-coloured
spots near the apex. The dermal membrane, or outer skin, seems to be
continuous over the stem and the globose head. At present, there is no
external evidence of an expanded pileus and gills; a longitudinal
section at this stage shows that the gills are being developed, that
the pileus is assuming its cap-like form, that the membrane stretching
from the stem to the edge of the young pileus is separating from the
edge of the gills, and forming a _veil_, which, in course of time,
will separate below and leave the gills exposed. When, therefore, the
mushroom has arrived almost at maturity, the pileus expands, and in
this act the veil is torn away from the margin of the cap, and remains
for a time like a collar around the stem. Fragments of the veil often
remain attached to the margin of the pileus, and the collar adherent
to the stem falls back, and thenceforth is known as the _annulus_ or
ring. We have in this stage the fully-developed hymenophore,--the stem
with its ring, supporting an expanded cap or pileus, with gills on the
under surface bearing the hymenium.[B] A longitudinal section cut
through the pileus and down the stem, gives the best notion of the
arrangement of the parts, and their relation to the whole. By this
means it will be seen that the pileus is continuous with the stem,
that the substance of the pileus descends into the gills, and that
relatively the substance of the stem is more fibrous than that of the
pileus. In the common mushroom the ring is very distinct surrounding
the stem, a little above the middle, like a collar. In some Agarics
the ring is very fugacious, or absent altogether. The form of the
gills, their mode of attachment to the stem, their colour, and more
especially the colour of the spores, are all very important features
to be attended to in the discrimination of species, since they vary in
different species. The whole substance of the Agaric is cellular. A
longitudinal slice from the stem will exhibit under the microscope
delicate tubular cells, the general direction of which is lengthwise,
with lateral branches, the whole interlacing so intimately that it is
difficult to trace any individual thread very far in its course. It
will be evident that the structure is less compact as it approaches
the centre of the stem, which in many species is hollow. The
_hymenium_ is the spore-bearing surface, which is exposed or naked,
and spread over the gills. These plates are covered on all sides with
a delicate membrane, upon which the reproductive organs are developed.
If it were possible to remove this membrane in one entire piece and
spread it out flat, it would cover an immense surface, as compared
with the size of the pileus, for it is plaited or folded like a lady's
fan over the whole of the gill-plates, or lamellæ, of the fungus.[C]
If the stem of a mushroom be cut off close to the gills, and the cap
laid upon a sheet of paper, with the gills downwards, and left there
for a few hours, when removed a number of dark radiating lines will be
deposited upon the paper, each line corresponding with the interstices
between one pair of gills. These lines are made up of spores which
have fallen from the hymenium, and, if placed under the microscope,
their character will at once be made evident. If a fragment of the
hymenium be also submitted to a similar examination, it will be found
that the whole surface is studded with spores. The first peculiarity
which will be observed is, that these spores are almost uniformly in
groups of four together. The next feature to be observed is, that each
spore is borne upon a slender stalk or sterigma, and that four of
these sterigmata proceed from the apex of a thicker projection, from
the hymenium, called a _basidium_, each basidium being the supporter
of four sterigmata, and each sterigma of a spore.[D] A closer
examination of the hymenium will reveal the fact that the basidia are
accompanied by other bodies, often larger, but without sterigmata or
spores; these have been termed _cystidia_, and their structure and
functions have been the subject of much controversy.[E] Both kinds of
bodies are produced on the hymenium of most, if not all, the
Agaricini.
[Illustration: FIG. 2.--Section of Common Mushroom.]
[Illustration: FIG. 3.--_a._ Sterile cells. _b._ Basidia. _c._ Cystidium.
From _Gomphidius_ (de Seynes).]
The basidia are usually expanded upwards, so as to have more or less
of a clavate form, surmounted by four slender points, or tubular
processes, each supporting a spore; the contents of these cells are
granular, mixed apparently with oleaginous particles, which
communicate through the slender tubes of the spicules with the
interior of the spores. Corda states that, although only one spore is
produced at a time on each sporophore, when this falls away others are
produced in succession for a limited period. As the spores approach
maturity, the connection between their contents and the contents of
the basidia diminishes and ultimately ceases. When the basidium which
bears mature spores is still well charged with granular matter, it may
be presumed that the production of a second or third series of spores
is quite possible. Basidia exhausted entirely of their contents, and
which have become quite hyaline, may often be observed.
The cystidia are usually larger than the basidia, varying in size and
form in different species. They present the appearance of large
sterile cells, attenuated upwards, sometimes into a slender neck.
Corda was of opinion that these were male organs, and gave them the
name of _pollinaires_. Hoffmann has also described[F] both these
organs under the names of _pollinaria_ and _spermatia_, but does not
appear to recognize in them the sexual elements which those names
would indicate; whilst de Seynes suggests that the cystidia are only
organs returned to vegetative functions by a sort of hypertrophy of
the basidia.[G] This view seems to be supported by the fact that, in
the section _Pluteus_ and some others, the cystidia are surmounted by
short horns resembling sterigmata. Hoffmann has also indicated[H] the
passage of cystidia into basidia. The evidence seems to be in favour
of regarding the cystidia as barren conditions of basidia. There are
to be found upon the hymenium of Agarics a third kind of elongated
cells, called by Corda[I] basilary cells, and by Hoffmann "sterile
cells," which are either equal in size or smaller than the basidia,
with which also their structure agrees, excepting in the development
of spicules. These are the "proper cells of the hymenium" of Léveillé,
and are simply the terminal cells of the gill structure--cells which,
under vigorous conditions, might be developed into basidia, but which
are commonly arrested in their development. As suggested by de Seynes,
the hymenium seems to be reduced to great simplicity, "one sole and
self-same organ is the basis of it; according as it experiences an
arrest of development, as it grows and fructifies, or as it becomes
hypertrophied, it gives us a paraphyse, a basidium, or a cystidium--in
other terms, atrophied basidium, normal basidium and hypertrophied
basidium; these are the three elements which form the hymenium."[J]
The only reproductive organs hitherto demonstrated in Agarics are the
spores, or, as sometimes called, from their method of production,
_basidiospores_.[K] These are at first colourless, but afterwards
acquire the colour peculiar to the species. In size and form they are,
within certain limits, exceedingly variable, although form and size
are tolerably constant in the same species. At first all are globose;
as they mature, the majority are ovoid or elliptic; some are fusiform,
with regularly attenuated extremities. In _Hygrophorus_ they are
rather irregular, reniform, or compressed in the middle. Sometimes the
external surface is rough with more or less projecting warts. Some
mycologists are of opinion that the covering of the spore is double,
consisting of an _exospore_ and an _endospore_, the latter being very
fine and delicate. In other orders the double coating of the spore has
been demonstrated. When the spore is coloured, the external membrane
alone appears to possess colour, the endospore being constantly
hyaline. It may be added here, that in this order the spore is simple
and unicellular. In _Lactarius_ and _Russula_ the trama, or inner
substance, is vesicular. True latex vessels occur occasionally in
_Agaricus_, though not filled with milk as in _Lactarius_.
[Illustration: FIG. 4.--_Polyporus giganteus_ (reduced).]
POLYPOREI.--In this order the gill plates are replaced by tubes or
pores, the interior of which is lined by the hymenium; indications
of this structure having already been exhibited in some of the
lower _Agaricini._ In many cases the stem is suppressed. The
substance is fleshy in _Boletus_, but in _Polyporus_ the greater
number of species are leathery or corky, and more persistent. The
basidia, spicules, and quaternate spores agree with those of
_Agaricini_.[L] In fact there are no features of importance which
relate to the hymenium in any order of _Hymenomycetes_ (the
_Tremellini_ excepted) differing from the same organ in _Agaricini_,
unless it be the absence of _cystidia_.
[Illustration: FIG. 5.--_Hydnum repandum._]
HYDNEI.--Instead of pores, in this order the hymenium is spread over
the surface of spines, prickles, or warts.[M]
AURICULARINI.--The hymenium is more or less even, and in--
CLAVARIEI the whole fungus is club-shaped, or more or less intricately
branched, with the hymenium covering the outer surface.
[Illustration: FIG. 6.--_Calocera viscosa._]
[Illustration: FIG. 7.--_Tremella mesenterica._]
TREMELLINI.--In this order we have a great departure from the
character of the substance, external appearance, and internal
structure of the other orders in this family. Here we have a
gelatinous substance, and the form is lobed, folded, convolute, often
resembling the brain of some animal. The internal structure has been
specially illustrated by M. Tulasne,[N] through the common species,
_Tremella mesenterica_. This latter is of a fine golden yellow colour,
and rather large size. It is uniformly composed throughout of a
colourless mucilage, with no appreciable texture, in which are
distributed very fine, diversely branched and anastomosing filaments.
Towards the surface, the ultimate branches of this filamentous network
give birth, both at their summits and laterally, to globular cells,
which acquire a comparatively large size. These cells are filled with
a protoplasm, to which the plant owes its orange colour. When they
have attained their normal dimensions, they elongate at the summit
into two, three, or four distinct, thick, obtuse tubes, into which the
protoplasm gradually passes. The development of these tubes is unequal
and not simultaneous, so that one will often attain its full
dimensions, equal, perhaps, to three or four times the diameter of the
generative cell, whilst the others are only just appearing. By
degrees, as each tube attains its full size, it is attenuated into a
fine point, the extremity of which swells into a spheroidal cell,
which ultimately becomes a spore. Sometimes these tubes, or spicules,
send out one or two lateral branches, each terminated by a spore.
These spores (about ·006 to ·008 _mm._ diameter) are smooth, and
deposit themselves, like a fine white dust, on the surface of the
_Tremella_ and on its matrix. M. Léveillé[O] was of opinion that the
basidia of the Tremellini were monosporous, whilst M. Tulasne has
demonstrated that they are habitually tetrasporous, as in other of the
Hymenomycetes. Although agreeing in this, they differ in other
features, especially in the globose form of the basidia, mode of
production of the spicules, and, finally, the division of the basidia
into two, three, or four cells by septa which cut each other in their
axis. This division precedes the growth of the spicules. It is not
rare to see these cells, formed at the expense of an unilocular
basidium, become partly isolated from each other; in certain cases
they seem to have separated very early, they then become larger than
usual, and are grouped on the same filament so as to represent a kind
of buds. This phenomenon usually takes place below the level of the
fertile cells, at a certain depth in the mucous tissue of the
_Tremella_.
Besides the reproductive system here described, Tulasne also made
known the existence of a series of filaments which produce spermatia.
These filaments are often scattered and confused with those which
produce the basidia, and not distinguishable from them in size or any
other apparent characteristic, except the manner in which their
extremities are branched in order to produce the spermatia. At other
times the spermatia-bearing surface covers exclusively certain
portions of the fungus, especially the inferior lobes, imparting
thereto a very bright orange colour, which is communicated by the
layer of spermatia, unmixed with spores. These spots retain their
bright colour, while the remainder of the plant becomes pale, or
covered with a white dust. The spermatia are very small, spherical,
and smooth, scarcely equalling ·002 _mm._ They are sessile, sometimes
solitary, sometimes three or four together, on the slightly swollen
extremities of certain filaments of the weft of the fungus.[P] Tulasne
found it impossible to make these corpuscles germinate, and in all
essential particulars they agreed with the spermatia found in
ascomycetous fungi.
In the genus _Dacrymyces_, the same observer found the structure to
have great affinity with that of _Tremella_. The spores in the species
examined were of a different form, being oblong, very obtuse, slightly
curved (·013 - ·019 × ·004 - ·006 _mm._), at first unilocular, but
afterwards triseptate. The basidia are cylindrical or clavate, filled
with coloured granular matter; each of these bifurcates at the summit,
and gradually elongates into two very open branches, which are
attenuated above, and ultimately each is crowned by a spore. There are
to be found also in the species of this genus globose bodies,
designated "sporidioles" by M. Léveillé, which Tulasne took
considerable care to trace to their source. He thus accounts for
them:--Each of the cells of the spore emits exteriorly one or several
of these corpuscles, supported on very short and very slender
pedicels, which remain after the corpuscles are detached from them,
new corpuscles succeeding the first as long as there remains any
plastic matter within the spore. The pedicels are not all on the same
plane; they are often implanted all on the same, and oftenest on the
convex side of the reproductive body. These corpuscles, though placed
under the most favourable conditions, never gave the least sign of
vegetation, and Tulasne concludes that they are spermatia, analogous
to those produced in _Tremella_. The spores which produce spermatia
are not at all apt to germinate, whilst those which did not produce
spermatia germinated freely. Hence it would appear that, although all
spores seem to be perfectly identical, they have not all the same
function. The same observer detected also amongst specimens of the
_Dacrymyces_ some of a darker and reddish tint, always bare of spores
or spermatia on the surface, and these presented a somewhat different
structure. Where the tissue had turned red it was sterile, the
constituent filaments, ordinarily colourless, and almost empty of
solid matter, were filled with a highly-coloured protoplasm; they were
of less tenuity, more irregularly thick, and instead of only rarely
presenting partitions, and remaining continuous, as in other parts of
the plant, were parcelled out into an infinity of straight or curved
pieces, angular and of irregular form, especially towards the surface
of the fungus, where they compose a sort of pulp, varying in cohesion
according to the dry or moist condition of the atmosphere. All parts
of these reddish individuals seemed more or less infected with this
disintegration, the basidia divided by transverse diaphragms into
several cylindrical or oblong pieces, which finally become free.
Transitional conditions were also observed in mixed individuals. This
sterile condition is called by Tulasne "gemmiparous," and he believes
that it has ere now given origin to one or more spurious species, and
misled mycologists as to the real structure of perfect and fruitful
_Dacrymyces_.
PHALLOIDEI.--In this order the hymenium is at first enclosed within a
sort of peridium or universal volva, maintaining a somewhat globose or
egg-shape. This envelope consists of an outer and inner coat of
somewhat similar texture, and an intermediate gelatinous layer, often
of considerable thickness. When a section is made of the fungus,
whilst still enclosed in the volva, the hymenium is found to present
numerous cavities, in which basidia are developed, each surmounted by
spicules (four to six) bearing oval or oblong spores.[Q] It is very
difficult to observe the structure of the hymenium in this order, on
account of its deliquescent nature. As the hymenium approaches
maturity, the volva is ruptured, and the plant rapidly enlarges. In
_Phallus_, a long erect cellular stem bears the cap, over which the
hymenium is spread, and this expands enormously after escaping the
restraint of the volva. Soon after exposure, the hymenium deliquesces
into a dark mucilage, coloured by the minute spores, which drips from
the pileus, often diffusing a most loathsome odour for a considerable
distance. In _Clathrus_, the receptacle forms a kind of network. In
_Aseröe_, the pileus is beautifully stellate. In many the attractive
forms would be considered objects of beauty, were it not for their
deliquescence, and often foetid odour.[R]
[Illustration: FIG. 8.--Basidia and spores of _Phallus_.]
PODAXINEI.--This is a small but very curious group of fungi, in which
the peridium resembles a volva, which is more or less confluent with
the surface of the pileus. They assume hymenomycetal forms, some of
them looking like Agarics, Boleti, or species of _Hydnum_, with
deformed gills, pores, or spines; in _Montagnites_, in fact, the gill
structure is very distinct. The spores are borne in definite clusters
on short pedicels in such of the genera as have been examined.[S]
HYPOGÆI.--These are subterranean puff-balls, in which sometimes a
distinct peridium is present; but in most cases it consists entirely
of an external series of cells, continuous with the internal
structure, and cannot be correctly estimated as a peridium. The
hymenium is sinuous and convolute, bearing basidia with sterigmata and
spores in the cavities. Sometimes the cavities are traversed by
threads, as in the _Myxogastres_. The spores are in many instances
beautifully echinulate, sometimes globose, at others elongated, and
produced in such numbers as to lead to the belief that their
development is successive on the spicules. When fully matured, the
peridia are filled with a dusty mass of spores, so that it is scarcely
possible in this condition to gain any notion of the structure. This
is, indeed, the case with nearly all _Gasteromycetes_. The hypogæous
fungi are curiously connected with _Phalloidei_ by the genus
_Hysterangium_.
[Illustration: FIG. 9.--Basidia and spores of _Lycoperdon_.]
TRICHOGASTRES.[T]--In their early stages the species contained in
this group are not gelatinous, as in the _Myxogastres_, but are
rather fleshy and firm. Very little has been added to our knowledge
of structure in this group since 1839 and 1842, when one of us
wrote to the following effect:--If a young plant of _Lycoperdon
coelatum_ or _L. gemmatum_ be cut through and examined with a common
pocket lens, it will be found to consist of a fleshy mass,
perforated in every direction with minute elongated, reticulated,
anastomosing, labyrinthiform cavities. The resemblance of these to the
tubes of _Boleti_ in an early stage of growth, first led me to
suspect that there must be some very close connection between them.
If a very thin slice now be taken, while the mass is yet firm, and
before there is the slightest indication of a change of colour, the
outer stratum of the walls of these cavities is found to consist of
pellucid obtuse cells, placed parallel to each other like the pile
of velvet, exactly as in the young hymenium of an Agaric or
Boletus. Occasionally one or two filaments cross from one wall to
another, and once I have seen these anastomose. At a more advanced
stage of growth, four little spicules are developed at the tips of
the sporophores, all of which, as far as I have been able to observe,
are fertile and of equal height, and on each of these spicules a
globose spore is seated. It is clear that we have here a structure
identical with that of the true Hymenomycetes, a circumstance which
accords well with the fleshy habit and mode of growth. There is some
difficulty in ascertaining the exact structure of the species just
noticed, as the fruit-bearing cells, or sporophores, are very
small, and when the spicules are developed the substance becomes so
flaccid that it is difficult to cut a proper slice, even with the
sharpest lancet. I have, however, satisfied myself as to the true
structure by repeated observations. But should any difficulty arise
in verifying it in the species in question, there will be none in
doing so in _Lycoperdon giganteum_. In this species the fructifying
mass consists of the same sinuous cavities, which are, however,
smaller, so that the substance is more compact, and I have not seen
them traversed by any filaments. In an early stage of growth, the
surface of the hymenium, that is of the walls of the cavities,
consists of short threads composed of two or three articulations,
which are slightly constricted at the joints, from which, especially
from the last, spring short branchlets, often consisting of a
single cell. Sometimes two or more branchlets spring from the same
point. Occasionally the threads are constricted without any
dissepiments, the terminal articulations are obtuse, and soon swell
very much, so as greatly to exceed in diameter those on which they
are seated. When arrived at their full growth, they are somewhat
obovate, and produce four spicules, which at length are surmounted
each with a globose spore. When the spores are fully developed, the
sporophores wither, and if a solution of iodine be applied, which
changes the spores to a rich brown, they will be seen still adhering
by their spicules to the faded sporophores. The spores soon become
free, but the spicule often still adheres to them; but they are not
attached to the intermingled filaments. In _Bovista plumbea_, the
spores have very long peduncles.[U] As in the _Hymenomycetes_, the
prevailing type of reproductive organs consisted of quaternary
spores borne on spicules; so in _Gasteromycetes_, the prevailing
type, in so far as it is yet known, is very similar, in some cases
nearly identical, consisting of a definite number of minute spores
borne on spicules seated on basidia. In a very large number of
genera, the minute structure and development of the fructification
(beyond the mature spores) is almost unknown, but from analogy it
may be concluded that a method prevails in a large group like the
_Myxogastres_ which does not differ in essential particulars from that
which is known to exist in other groups. The difficulties in the way
of studying the development of the spores in this are far greater
than in the previous order.
[Illustration: FIG. 10.--_a._ Threads of _Trichia_. _b._ Portion further
magnified, with spores. _c._ Portion of spinulose thread.]