_SPERMOGONES._
IN addition to their spore-bearing spots, lichens have for some time
been known to possess other organs, termed _spermogones_, which are
probably concerned more or less in the reproductive process. The first
intimation of the existence of similar bodies in the entophytal fungi
originated with M. Unger in 1833, but it was left to Dr. de Bary and the
Messrs. Tulasne, twenty years later, to examine and determine
satisfactorily the nature and value of the spermogones of the Uredines.
It was at first believed that the smaller pustules—which sometimes
precede, and sometimes accompany, the cluster-cups and some other allied
fungi—were distinct species developed simultaneously therewith, or
members of a new genus, which, under the name of _Æcidiolum
exanthematum_, found a place in the mycologic system.
Without staying to trace the stages through which the elucidation of
their true nature proceeded, it will suffice for our purpose to tell
what is now known of these secondary organs; to accomplish which we must
stand greatly indebted to the independent researches of Messrs. de Bary
and Tulasne. It has been demonstrated that both these bodies, namely,
the primary organs or cluster-cups, and the secondary organs or
spermogones, are developed from the same mycelium; but the value of the
latter is still undetermined. If they possess any fecundative power, the
process has not been traced; or if they are in themselves reproductive,
they have not at present been seen to germinate. Their uses, therefore,
in the economy of the parasitic plant of which they are now known to
form a part is still a mystery, and they remain valueless in the
determination of genera and species. Any speculation which might regard
them as male organs would be premature, and without support in fact.
Hitherto only some species of the genera described in the foregoing
chapter, and others belonging to genera not hitherto named, have been
ascertained to possess spermogones. Of the former are the _Rœsteliæ_,
some species of _Æcidium_, as those of _Euphorbia_, &c., and
_Peridermium Pini_.
These spermogones are of a very simple structure—very delicate, indeed;
so much so, that they will scarcely bear preparation for demonstration.
De Bary states that they originate from plain, delicate, inarticulate
threads, about half the thickness of the mycelium (the root-like
branching fibres which form the fundamental stratum of fungoid growths),
which are developed in large quantities, and closely packed together.
These threads are compacted together so as to form an outer enveloping
integument or peridium, which is either globular or hemispherical (or in
some instances elongated), more or less immersed, and at length opening
at the apex (fig. 153) by a regularly formed minute ostiolum. The inner
wall of the peridium is covered with a thick forest of simple filaments
standing on end. From the summit of these filaments or sterigmata, the
spermatia are borne. These are either isolated or associated together in
strings or chaplets, are exceedingly minute, of an ovoid or oblong
shape, and are produced in such numbers as to fill the cavity of the
spermogone. Besides these, a viscid fluid is secreted, in which the
spermatia are immersed, and which is expelled with them from the orifice
of the peridium. According to the density of this fluid, or the
hygrometric state of the atmosphere, it appears sometimes in drops, and
sometimes oozing out in threads or cirrhi from the spermogones. To
compare minute things with gigantic, as a recent author has observed, it
resembles the lava issuing from the crater of a volcano. The colour of
this spermatiferous matter is commonly orange, but in some instances
brown, though not constantly of the same colour as the spores produced
from the same mycelium. This gelatinous substance is dissolved away from
the granular bodies which are immersed in it, by adding a little water
upon the slide on which the mass is placed for examination. The
granules, or spermatia, then exhibit those peculiar movements which have
been observed in the similar bodies in lichens, and fitly described as
“a sort of oscillating motion, as of a body attached at one extremity.”
The cause of this motion is at present uncertain, vibratile ciliæ, to
which similar movements are referred, being altogether absent; but
probably, as De Bary believes, the cause may be found in the influence
of exosmose.
The largest spermatia yet examined (those of _Peridermium Pini_) have a
length equal to 1/2500 of an inch, but their width seldom exceeds
1/100000 of an inch, whilst in others their length does not exceed the
width of those just named.
Messrs. Tulasne affirm that all these corpuscles, as well as the
mucilaginous fluid, evolve an appreciable odour, resembling that of the
pollen of the willow. M. Léveillé compares the odour to that of orange
flowers, and M. de Bary to that of the evening primrose.
SPERMOGONES
[Illustration:
FIG. 1.—_Æcidium grossulariæ_. _c._ Cluster-cups. _s._ Spermogones.
]
[Illustration:
FIG. 2.—Section of ripe spermogones of _Æcidium Euphorbiæ_. _s._
Spermatia. _a._ Sterigmatæ bearing spermatia (_De Bary_).
]
The spermogones do not always appear like pustules on the surface of the
leaves, for sometimes their presence is only indicated by minute
depressed punctures which are scarcely visible; generally, however, they
may be recognized by an obtuse, or otherwise a pointed, protuberance
that surmounts them. The margin of the orifice is sometimes furnished
with short hairs, but is more frequently ornamented with a pencil of
long hairs, which are stiff and erect, and of the colour of the enclosed
spermatia.
In many of the species of _Æcidium_ the cups are disposed in a more or
less regular circle, the centre of which is occupied by a group of
spermogones; at the same time, the corresponding spot on the opposite
surface of the leaf will frequently be found also occupied by other
spermogones—in some instances in greater number than on the same surface
of the leaf on which the cups are seated. This is the case in the
_Æcidium_ which is found upon the leaves of the coltsfoot, and that of
the honeysuckle.
Very bright orange-coloured spots may be observed in autumn (we have
encountered them often in August and September) upon the leaves of pear
trees, and which are covered with little tubercles, at first of the same
colour, but ultimately becoming brown. These pustules are so many
spermogones belonging to _Rœstelia cancellata_, a kind of cluster-cup
found in the same localities. These spots have long since been noticed,
and regarded as connected with the _Rœstelia_, but in what manner has
until recently been unknown. The Rev. M. J. Berkeley noticed them in the
English Flora in 1836, or at least the granulations on the upper
surfaces of the leaves bearing _R. cancellata_, _R. cornuta_, and _R.
lacerata_, and called them abortive pseudoperidia. Before this (in 1804)
they had been observed by Rebentisch. An examination of one of these
spots under a low power of the microscope, and afterwards a section of
one or more of the pustules, cut with a sharp razor, and viewed with a
higher power, will give an idea of the nature of the bodies we are
attempting to describe. During the past summer we have noticed very
similar orange spots on leaves of the berberry containing spermogones on
both surfaces, and these appeared before any cups had been found on that
plant. In this instance no cups were produced from the spots on the
leaves examined, and which were carefully noticed at intervals until
they withered and fell.
In some instances, as in _Rœstelia cornuta_, which is found on the
leaves of the mountain-ash, the cups are produced on the lower, but the
spermogones almost exclusively on the upper surface.
The spermogones of _Peridermium Pini_ are white, few in number, and are
developed, not only in the spring, but sometimes reappear in the autumn
upon the same leaves that produced them at the commencement of the year.
In such instances as those of the _Æcidium_ of the spurge, and also the
goatsbeard, in which the cluster-cups are arranged in no appreciable
order, the spermogones are scattered amongst them, and even in some
instances appear on different leaves. The spermogones are common on the
wood spurge in spring, scattered over both surfaces of the leaves before
the cluster-cups make their appearance, and gradually these latter are
developed amongst them, commencing from the apex of the leaves and
proceeding in the order of their development towards the base. In this
instance the spermogones are bright yellow, as are afterwards the cups
and spores of the _Æcidium_. In most instances the appearance of the
spermogones precedes that of the sporiferous organs, but the latter
follow sufficiently speedy for perfect development before the decadence
of the spermogones takes place.
After the expulsion of the spermatia and the fluid which accompanies
them, the whole mass dries up; and where many spermogones have been
clustered together in the same spot a brown homogeneous crust is formed
upon the epidermis; where they are produced singly, a brownish
incrustation is visible about the mouth of each spermogone.
Re-agents applied to the spermogones whilst in full vitality indicate
the presence of a considerable amount of a protein substance, which,
with sugar and sulphuric acid, produces a deep purple red colour.
From what we have already stated of the method of occurrence of these
organs, the following is the only order, apparently, preserved in their
development, although no definite rules can at present be affirmed. The
spore spots of cluster-cups are generally found upon the under surfaces
of the leaves on which they are produced, and the spermogones are most
numerous on the upper. When both the cluster-cups and the spermogones
appear in the same group on the same surface, the spermogones commonly
occupy the centre, and the cups are arranged in a circular manner about
them. In other, and fewer instances, both organs stand together
indiscriminately upon the same surface.
The spermogones are also developed centrifugally, at least so far as at
present observed, for when they are produced in a cluster the central
one first opens and discharges its contents, and thus the development
proceeds outwards from the centre to the circumference. When the
spermogones are scattered, as in those of _Euphorbia_, they are first
observed at the apex of the leaf, whence they are developed in
succession towards the base. The latter should be sought for on the
young plants of the wood spurge in March or April, at which time we have
found them abundant at Darenth wood, near Dartford.
It must not be concluded, from the fact that we have not yet adverted to
spermogones in connection with other fungi, that they are peculiar to
the _Æcidiacei_. Such is by no means the case. As we have hereafter
described other genera and species in which spermogones occur, it would
be out of place to enter upon further details here. Let it suffice
therefore that we state that they have been found in members of the
genera, _Aregma_, _Triphragmium_, _Puccinia_, _Lecythea_, _Trichobasis_,
and _Uredo_, but they have been found much more generally in _Rœstelia_
and _Æcidium_ than in any other genus.
As comparatively little is yet known of these bodies, a fair field is
open to the enterprising microscopist, with time at his disposal, and a
good store of perseverance, to win for himself renown in the discovery
of fresh facts, and the elucidation of some of the mysteries which yet
enshroud these interesting organisms. From the foregoing pages he will
learn the direction in which his researches should tend, and he may be
assured that every new fact is of importance when carefully ascertained.
[Illustration:
Plate II.
W. West imp.
]
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