of copulation in _Ascobolus furfuraceus_, or _Peziza melanoloma_, he
was more successful with _Peziza omphalodes_. As early as 1860 he
recognized the large globose, sessile, and grouped vesicles which
originate the fertile tissue, but did not comprehend the part which
these macrocysts were to perform. Each of these emits from its summit
a cylindrical tube, generally flexuous, but always more or less bent
in a crozier shape, sometimes attenuated at the extremity. Thus
provided, these utricles resemble so many tun-shaped, narrow-necked
retorts, filled with a granular thick roseate protoplasm. In the
middle of these, and from the same filaments, are generated elongated
clavate cells, with paler contents, more vacuoles, which Tulasne names
_paracysts_. These, though produced after the _macrocysts_, finally
exceed them in height, and seem to carry their summit so as to meet
the crozier-like prolongations. It would be difficult to determine to
which of these two orders of cells belongs the initiative of
conjugation. Sometimes the advance seems to be on one side, and
sometimes on the other. However this may be, the meeting of the
extremity of the connecting tube with the summit of the neighbouring
paracyst is a constant fact, observed over and over again a hundred
times. There is no real junction between the dissimilar cells above
described, except at the very limited point where they meet, and there
a circular perforation may be discerned at the end, defined by a round
swelling, which is either barely visible or sometimes very decided.
Everywhere else the two organs may be contiguous, or more or less near
together, but they are free from any adherence whatever. If the
plastic matters contained in the conjugated cells influence one
another reciprocally, no notable modification in their appearance
results at first. The large appendiculate cell seems, however, to
yield to its consort a portion of the plasma it contains. One thing
only can be affirmed from these phenomena, that the conjugated cells,
especially the larger, wither and empty themselves, while the upright
compressed filaments, which will ultimately constitute the asci,
increase and multiply.[M]
[Illustration: FIG. 100.--Conjugation in _Peziza omphalodes_. (Tulasne.)]
[Illustration: FIG. 100a.--Formation of conceptacle in _Erysiphe_.]
Certain phenomena concerned in the development of the _Erysiphei_ belong
also to this connection. The mycelium of _Erysiphe cichoracearum_, like
that of other species, consists of branched filaments, crossed in all
directions, which adhere as they climb to the epidermis of the plant on
which the fungus lives as a parasite. The perithecia are engendered
where two filaments cross each other. These swell slightly at this
point, and each emits a process which imitates a nascent branch, and
remains upright on the surface of the epidermis. The process
originating from the inferior filament soon acquires an oval form and
a diameter double that of the filament; then it becomes isolated from
it by a septum, and constitutes a distinct cell, which De Bary[N]
terms an oocyst. The appendage which proceeds from the inferior filament
always adheres intimately to this cell, and elongates into a slender
cylindrical tube, which terminates in an obtuse manner at the summit
of the same cell. At its base it is also limited by a septum, and soon
after another appears a little below its extremity at a point
indicated beforehand by a constriction. This new septum defines a
terminal short obtuse cell, the antheridium, which is thus borne on a
narrow tube like a sort of pedicel. Immediately after the formation of
the antheridia new productions show themselves, both around the oocyst
and within it. Underneath this cell eight or ten tubes are seen to
spring from the filament which bears it; these join themselves by the
sides to each other and to the pedicel of the antheridium, while they
apply their inner face to the oocyst, above which their extremities soon
meet. Each of the tubes is then divided by transverse septa into two
or three distinct cells, and in this manner the cellular walls of the
perithecia come into existence.
During this time the oocyst enlarges and divides, without its being
possible precisely to determine the way in which it happens, into a
central cell and an outer layer, ordinarily simple, of smaller
cells, contiguous to the general enveloping wall. The central cell
becomes the single ascus, which is characteristic of the species,
and the layer which surrounds it constitutes the inner wall of its
perithecium. The only changes afterwards observed are the increase
in size of the perithecium, the production of the root-like filaments
which proceed from its outer wall, the brown tint which it assumes,
and finally the formation of the sporidia in the ascus. The
antheridium remains for a long time recognizable without undergoing
any essential modification, but the dark colour of the perithecium
soon hides it from the observer's eye. De Bary thinks that he is
authorized in assuming the probability that the conceptacles and
organs of fructification of others of the _Ascomycetes_, including
the _Discomycetes_ and the _Tuberacei_, are the results of sexual
generation.
Certain phenomena which have been observed amongst the _Coniomycetes_
are cited as examples of sexual association. Amongst these may be
named the conjugation of the slender spores of the first generation,
produced on the germinating threads of _Tilletia_,[O] and similar
acts of conjugation, as observed in some species of _Ustilago_.
Whether this interpretation should be placed on those phenomena in the
present condition of our knowledge is perhaps an open question.
[Illustration: FIG. 101.--_Tilletia caries_ with conjugating cells.]
Finally, the spermogonia must be regarded as in some occult manner,
which as yet has baffled detection, influencing the perfection of
sporidia[P] In _Rhytisma_, found on the leaves of maple and willow,
black pitchy spots at first appear, which contain within them a golden
pulp, in which very slender corpuscles are mixed with an abundant
mucilage. These corpuscles are the spermatia, which in _Rhytisma
acerinum_ are linear and short, in _Rhytisma salicinum_ globose. When
the spermatia are expelled, the stroma thickens for the production of
asci and sporidia, which are afterwards developed during the autumn
and winter.
Several of the species of _Hysterium_ also possess spermogonia,
notably _H. Fraxini_, which may be distinguished from the ascigerous
perithecia with which they are associated by their smaller size and
flask-like shape. From these the spermatia are expelled long before
the maturity of the spores. In _Hypoderma virgultorum_, _H.
commune_, and _H. scirpinum_, the spermogonia are small depressed
black capsules, which contain an abundance of minute spermatia.
These were formerly regarded as distinct species, under the name of
_Leptostroma_. In _Stictis ocellata_ a great number of the tubercles
do not pass into the perfect state until after they have produced
either linear, very short spermatia, or stylospores, the latter
being reproductive bodies of an oblong shape, equal in size to the
perfect sporidia. Some of the tubercles never pass beyond this stage.
Again, there is a very common fungus which forms black discoid spots
on dead holly leaves, called _Ceuthospora phacidioides_, figured by
Greville in his "Scottish Cryptogamic Flora," which expels a profusion
of minute stylospores; but later in the season, instead of these, we
find the asci and sporidia of _Phacidium ilicis_, so that the two are
forms and conditions the one of the other.
In _Tympanis conspersa_ the spermogonia are much more commonly met
with than the complete fruit. There is a great external resemblance in
them to the ascigerous cups, but there is no evidence that they are
ever transformed into such. The perfect sporidia are also very minute
and numerous, being contained in asci borne in cups, which usually
surround the spermogonia.
In several species of _Dermatea_ the stylospores and spermatia
co-exist, but they are disseminated before the appearance of the
ascigerous receptacles, yet they are produced upon a common stroma not
unlike that of _Tubercularia_.
In its early stage the common and well-known _Bulgaria inquinans_,
which when mature looks like a black _Peziza_, is a little tubercle,
the whole mass of which is divided into ramified lobes, the
extremities of which become, towards the surface of the tubercle,
receptacles from whence escape waves of spermatia which are
colourless, or stylospores mixed with them which are larger and nearly
black.
Amongst the _Sphæriacei_ numerous instances might be cited of minute
stylosporous bodies in consort with, or preceding, the ascigerous
receptacles. A very familiar example may be found at the base of old
nettle stems in what has been named _Aposphæria acuta_, but which
truly are only the stylospores of the _Sphæria coniformis_, the
perithecia of which flourish in company or in close proximity to them.
Most of these bodies are so minute, delicate, and hyaline that the
difficulties in the way of tracing them in their relations to the
bodies with which they are associated are very great. Nevertheless
there is strong presumption in favour of regarding some of them as
performing the functions which the name applied to them indicates.
Professor de Bary cautiously refrains from accepting spermatia other
than as doubtful or at least uncertain sexual bodies.[Q] He says that
the Messrs. Tulasne have supposed that the spermogonia represented the
male sex, and that the spermatia were analogous to spermatozoids.
Their opinion depends on two plausible reasons,--the spermatia, in
fact, do not germinate, and the development of the spermogonia
generally precedes the appearance of the sporophorous organs, a double
circumstance which reminds us of what is known of the spermatozoids
and antheridia of other vegetables. It remained to discover which were
the female organs which underwent fecundation from the spermatia.
Many organs placed at first amongst spermatia have been recognized by
M. Tulasne as being themselves susceptible of germination, and
consequently ought to take their place among legitimate spores. Then
it must be considered that very many spores can only germinate under
certain conditions. It is, therefore, for the present a doubtful
question whether there exist really any spermatia incapable of
germination, or if the default of germination of these corpuscles does
not rather depend on the experiments hitherto attempted not having
included the conditions required by the phenomena. Moreover, as yet no
trace has been discovered of the female organs which are specially
fecundated by the spermatia.
Finally, there exist in the _Ascomycetes_ certain organs of
reproduction, diverse spore-bearing apparatus, pycnidia, and others,
which, like the spermogonia, usually precede ascophorous fruits. The
real nature of the spermogonia and spermatia should therefore be
regarded as, at present, very uncertain; as regards, however, the
spermatia which have never been seen to germinate, perhaps it is as
well not to absolutely reject the first opinion formed concerning
them, or perhaps they might be thought to perform the part of
androspores, attributing to that expression the meaning which
Pringsheim gives it in the _Conferoæ_. The experiments performed with
the spermatia which do not germinate, and with the spermogonia of the
Uredines, do not, at any rate, appear to justify the reputed masculine
or fecundative nature of these organs. The spermogonia constantly
accompany or precede fruits of _Æcidium_, whence naturally follows the
presumption that the first are in a sexual relation to the second.
Still, when Tulasne cultivated _Endophyllum sempervivum_, he obtained
on some perfectly isolated rosettes of _Sempervivum_ some _Æcidium_
richly provided with normal and fertile spores, without any trace of
spermogonia or of spermatia.
[A] M. Tulasne has devoted a chapter to the spermogonia of the
Uredines in his memoir, to which we have already alluded.
[B] Oeersted, in "Verhandl der König. Dän. Gesell. Der Wissensch,"
1st January, 1865; De Bary, "Handbuch der Physiol. Botanik"
(1866), p. 172; "Annales des Sci. Nat." (5^me sér.), vol. v.
(1866), p. 366.
[C] Van Tieghem and Le Monnier, in "Annales des Sci. Nat." (1873),
vol. xvii. p. 261.
[D] Brefeld, "Bot. Unt. uber Schimmelpilze," p. 31.
[E] De Bary, "Morphologie und Physiologie der Pilze," cap. 5, p. 160;
"Ann. des Sci. Nat." (1866), p. 343.
[F] Cornu, in "Ann. des Sci. Nat." (5^me sér.), vol. xv. p. 1
(1872).
[G] Pringsheim's "Jahrbucher," vol. ii. p. 169.
[H] De Bary, in "Annales des Sciences Naturelles" (5^me sér.), vol.
v. (1866), p. 343; Hoffmeister's "Handbook" (Fungi), cap. v. p.
155.
[I] De Bary, in "Annales des Sci. Nat." (4^me sér.), vol. xx. p.
129.
[J] De Bary, in "Annales des Sciences Naturelles" (5^me sér.), p.
343.
[K] Woronin, in De Bary's "Beitr. zur. Morph. und Physiol. der
Pilze," ii. (1866), pp. 1-11.
[L] Tulasne, "Ann. des Sci. Nat." (5^me sér.), October, 1866, p.
211.
[M] Tulasne, "On the Phenomena of Copulation in certain Fungi," in
"Ann. des Sci. Nat." (1866), p. 211.
[N] De Bary, "Morphologie und Phys. der Pilze," cap. v., p. 162.
[O] Berkeley, in "Journ. Hort. Soc." vol ii. p. 107; Tulasne, "Ann.
d. Sc. Nat." (4^me sér.), vol. ii. tab. 12.
[P] Tulasne, "New Researches on the Reproductive Apparatus of Fungi;"
"Comptes Rendus," vol. xxxv. (1852), p. 841.
[Q] De Bary, "Morphologie und Physiologie der Pilze," cap. v. p.
168.
IX.
POLYMORPHISM.
A great number of very interesting facts have during late years been
brought to light of the different forms which fungi assume in the
course of their development. At the same time, we fear that a great
many assumptions have been accepted for fact, and supposed connections
and relations between two or three or more so-called species,
belonging to different genera, have upon insufficient data been
regarded as so many states or conditions of one and the same plant.
Had the very pertinent suggestions of Professor de Bary been more
generally acted upon, these suspicions would have been baseless. His
observations are so valuable as a caution, that we cannot forbear
prefacing our own remarks on this subject by quoting them.[A] In order
to determine, he says, whether an organic form, an organ, or an
organism, belongs to the same series of development as another, or
that which is the same is developed from it, or _vice versâ_, there is
only one way, viz., to observe how the second grows out of the first.
We see the commencement of the second begin as a part of the first,
perfect itself in connection with it, and at last it often becomes
independent; but be it through spontaneous dismembering from the
first, or that the latter be destroyed and the second remains, both
their disunited bodies are always connected together in organic
continuity, as parts of a whole (single one) that can cease earlier or
later.
By observing the organic continuity, we know that the apple is the
product of development of an apple-tree, and not hung on it by
chance, that the pip of an apple is a product of the development of
the apple, and that from the pip an apple-tree can at last be
developed, that therewith all these bodies are members of a sphere of
development or form. It is the same with every similar experience of
our daily life, that where an apple-tree stands, many apples lie on
the ground, or that in the place where apple-pips are sown seedlings,
little apple-trees, grow out of the ground, is not important to our
view of the course of development. Every one recognizes that in his
daily life, because he laughs at a person who thinks a plum which
lies under an apple-tree has grown on it, or that the weeds which
appear among the apple seedlings come from apple-pips. If the
apple-tree with its fruit and seed were microscopically small, it
would not make the difference of a hair's breadth in the form of the
question or the method of answering it, as the size of the object
can be of no importance to the latter, and the questions which
apply to microscopical fungi are to be treated in the same manner.
If it then be asserted that two or several forms belong to a series of
development of one kind, it can only be based on the fact of their
organic continuity. The proof is more difficult than in large plants,
partly because of the delicacy, minuteness, and fragility of the
single parts, particularly the greater part of the mycelia, partly
because of the resemblance of the latter in different species, and
therefore follows the danger of confusing them with different kinds,
and finally, partly in consequence of the presence of different kinds
in the same substratum, and therefore the mixture not only of
different sorts of mycelia, but also that different kinds of spores
are sown. With some care and patience, these difficulties are in no
way insurmountable, and they must at any rate be overcome; the organic
continuity or non-continuity must be cleared up, unless the question
respecting the course of development, and the series of forms of
special kinds, be laid on one side as insolvable.
Simple and intelligible as these principles are, they have not always
been acted upon, but partly neglected, partly expressly rejected, not
because they were considered false, but because the difficulties of
their application were looked upon as insurmountable. Therefore
another method of examination was adopted; the spores of a certain
form were sown, and sooner or later they were looked after to see what
the seed had produced--not every single spore--but the seed _en
masse_, that is, in other words, what had grown on that place where
the seed had been sown. As far as it relates to those forms which are
so widely spread, and above all grow in conjunction with one
another--and that is always the case in the specimens of which we
speak--we can never be sure that the spores of the form which we mean
to test are not mingled with those of another species. He who has made
an attentive and minute examination of this kind knows that we may be
sure to find such a mixture, and that such an one was there can be
afterwards decidedly proved. From the seed which is sown, these
spores, for which the substratum was most suitable, will more easily
germinate, and their development will follow the more quickly. The
favoured germs will suppress the less favoured, and grow up at their
expense. The same relation exists between them as between the seeds,
germs, and seedlings of a sown summer plant, and the seeds which have
been undesignedly sown with it, only in a still more striking manner,
in consequence of the relatively quick development of the mildew
fungus.
Therefore, that from the latter a decided form, or a mixture of
several forms, is to be found sown on one spot, is no proof of
their generic connection with one which has been sown for the
purpose of experiments; and the matter will only be more confused
if we call imagination to our aid, and place the forms which are
found near one another, according to a real or fancied resemblance,
in a certain series of development. All those statements on the
sphere of form and connection, which have for their basis such a
superficial work, and are not based on the clear exposition of the
continuity of development, as by the origin of the connection of
the _Mucor_ with _Penicillium_, _Oidium lactis_ and _Mucor_, _Oidium_
and _Penicillium_, are rejected as unfounded.
A source of error, which can also interfere in the last-named
superficial method of cultivation for experiments, is, viz., that
heterogeneous unwished-for spores intrude themselves from without,
among the seed which is sown, but that has been until now quite
disregarded. It is of great importance in practice, but in truth, for
our present purpose, synonymous with what we have already written.
Those learned in the science of this kind of culture lay great stress
on its importance, and many apparatuses have been constructed, called
"purely cultivating machines," for the purpose of destroying the
spores which are contained in the substratum, and preventing the
intrusion of those from without. The mixture in the seed which is sown
has of course not been obviated. These machines may, perhaps, in every
other respect, fulfil their purpose, but they cannot change the form
of the question, and the most ingeniously constructed apparatus cannot
replace the attention and intellect of the observer.[B]
Two distinct kinds of phenomena have been grouped under the term
"polymorphy." In one series two or more forms of fruit occur
consecutively or simultaneously on the same individual, and in the
other two or more forms appear on a different mycelium, on a different
part of the same plant, or on a matrix wholly distinct and different;
in the latter case the connection being attested or suspected
circumstantially, in the former proved by the method suggested by De
Bary. It will at once be conceded that in cases where actual growth
and development substantiate the facts the polymorphy is undoubted,
whilst in the other series it can at best be little more than
suspected. We will endeavour to illustrate both these series by
examples.
One of the first and earliest suspected cases of dualism, which long
puzzled the older mycologists, was observed amongst the Uredines, and
many years ago it was held that there must be some mysterious
association between the "red rust" (_Trichobasis ruligo vera_) of
wheat and grasses and the "corn mildew" (_Puccinia graminis_) which
succeeded it. The simple spored rust first makes its appearance, and
later the bilocular "mildew." It is by no means uncommon to find the
two forms in the same pustule. Some have held, without good reason,
that the simple cells became afterwards divided and converted into
_Puccinia_, but this is not the case; the uredo-spores are always
simple, and remain so except in _Uredo linearis_, where every
intermediate stage has been observed. Both are also perfect in their
kind, and capable of germination.
What the precise relations between the two forms may be has as yet
never been revealed to observers, but that the two forms belong to one
species is not now doubted. Very many species of _Puccinia_ have
already been found associated with a corresponding _Trichobasis_, and
of _Phragmidium_ with a relative _Lecythea_, but it may be open to
grave doubt whether some of the very many species associated by
authors are not so classed upon suspicion rather than observation. We
are ready to admit that the evidence is strong in favour of the
dimorphism of a large number of species--it _may_ be in all, but this
awaits proof, or substantial presumption on good grounds. Up to the
present we know that there are species of _Trichobasis_ which have
never been traced to association with a _Puccinia_, and doubtless
there will be species of _Puccinia_ for which no corresponding _Uredo_
or _Trichobasis_ can be found.
Tulasne remarks, in reference to _Puccinia sonchi_, in one of his
memoirs, that this curious species exhibits, in effect, that a
_Puccinia_ may unite three sorts of reproductive bodies, which, taking
part, constitute for the mycologists of the day three entirely
different plants--a _Trichobasis_, a _Uromyces_, and a _Puccinia_. The
Uredines are not less rich, he adds, in reproductive bodies of divers
sorts than the _Pyrenomycetes_ and the _Discomycetes_; and we should
not be surprised at this, since it seems to be a law, almost constant
in the general harmony of nature, that the smaller the organized
beings are, the more their races are prolific.
In _Puccinia variabilis_, Grev., it is common to find a unicellular
form, species of _Trichobasis_, in the same pustules. A like
circumstance occurs with _Puccinia violarum_, Link., and _Trichobasis
violarum_, B.; with _Puccinia fallens_, C., and _Trichobasis fallens_,
Desm.; also with _Puccinia menthæ_, P., and _Trichobasis Labiatarum_,
D. C. In _Melampsora_, again, the prismatic pseudospores of
_Melampsora salicina_, Lev., are the winter fruits of _Lecythea
caprearum_, Lev., as those of _Melampsora populina_, Lev., are of
_Lecythea populina_, Lev. In the species of _Lecythea_ themselves will
be found, as De Bary[C] has shown, hyaline cysts of a larger size,
which surround the pseudospores in the pustules in which they are
developed.