144
SYDNEY H. VINES.
crackling noise.
The fasciculi of the first order are distinguished by their aspect as well as by the great resistance they
offer to the probe, which may need to be aided by a few strokes
of a knife. The fasciculi of the second order are distinguishable by their fineness and the readiness with which they break.
They may be further recognised on membranous layers which
have been entirely detached, and which, though apparently
smooth, give to the finger when lightly passed over the surface
the sensation of numberless points so closely set together as to
feel like a fine brush. Moreover, when viewed with a magnifying power of 40 diameters, they are seen to be perpendicular to
the surface of the detached layer, whereas the broken ends of the
first order of fasciculi are not only larger, but lie flat on the
fibrous layer.
I cannot doubt, that the objects here described are really the
perforating fibres; at the same time, I cannot well conceive that
those I have met with, small and soft as they are, should feel
under the finger like the hairs of a brush, however fine.
Respecting Dr. dementi's note, I have further only to point
out that he is in error when he asserts, as he does (p. 12), that
I did not notice the existence of the, fibres in question in flat or
tabular bones; and, in conclusion, I cannot help saying that
when I first observed these fibres I had no idea that they bad
been recognized before, still less did I imagine that the subject of
my observation would ever acquire such importance as to lead to
a formal claim of priority on the part of Italian science.—Yours
faithfully,
E. A. Schafer, Esq.,
Dec. 1, 1877.
W. SHABEEY.
RECENT RESEARCHES into the NATURE of LICHENS. By SYDNEY
H. VINES, B.A., B.Sc, Fellow and Lecturer of Christ's College,
Cambridge.
IN previous volumes of this Journal,1 Mr. Archer has traced
the history of the discussion upon Schwendener's theory from its
commencement in 1868 down to the end of the year 1873. I
will endeavour to maintain the continuity by briefly alluding to
the principal papers which have appeared upon the subject during
the intervening years, reserving the more recent publications for
a somewhat detailed account.
1
Vols. xiii and xiv.
RECENT RESEARCHES INTO THE NATURE OF LICHENS.
145
The last paper mentioned by Mr. Archer in his resume* is the
important one by Treub,1 published in November 1873. In the
' Flora' for January 1874, J. Muller hastens to combat the
results at which Treub had arrived. He regards the question as
still an open one, in spite of the recent publications of Treub and
Bornet, and maintains firmly the accuracy of his own observations in which he distinctly traced the development of the
gonidium from the hypha in Synalissa Saleoensis. He goes so
far as to say that, even if his own observations were inaccurate,
the new theory cannot be considered as established until it is
ascertained that the spermatia give rise to hyphoid and not to
gonidial products. Miiller's paper was soon followed by another
on the same side from the pen of Nylander.2 In it are repeated
most of the objections which this distinguished lichenologist had
already raised to the acceptance of Schwendener's theory, and
attention is particularly drawn to the fact that those Algse which
are regarded by the supporters of the theory as playing the part
of gouidia in various Lichens—such Algee, for instance, as Cora,
Dichonema, Scytonetna, Sirosiphon—are held by him to be themselves of the nature of Lichens. From this point of view,
the new theory of the structure of the lichen-thallus is simply
absurd.
In the July Number of the ' Popular Science Review/ of the
same year, the Rev. J. M. Crombie, comes forward as another
opponent of the new doctrine. In his article he gives a brief
history of the whole discussion, and sums up strongly in favour
of the older views. He is especially severe upon one of Bornet's
" strong points," viz., the identity of Protococcus viridis with
the gonidia of Physcia parietina. He admits the similarity existingl between these organisms, but cannot recognise it as
amounting to identity, for the gonidia of Physcia are larger and
multiply less actively, while Protococcus multiplies very rapidly.
Some facts, to which attention will subsequently be called, will
shew that these differences of habit do not suffice to prove these
organisms to be distinct.
Later on in the year an elaborate defence of the older views
was published by Korber.8 He lays down three propositions,
(1) that the tissue in which the gonidia of a Lichen are embedded is not of a fungoid nature; (SJ) that the gonidia are not
true AlgEej and (3) that Lichens are not the expressions of a
condition of parasitism. In support of his first proposition he
recalls the differences which Von Krempelhuber pointed out as
existing between the tissues of Lichens and those of Fungi, but
1
' Onderzoek. over de Natuur der Lichenen. Leiden.'
3
'Flora/ abstracted by the Rev. J. M. Crombie in 'Grevillea,' vol. ii.
3
'Zur Abwehr der Schwendener-Bornet'scben Elechtentheorie/ Breslau.
146
SYDNEY H. VINES.
admits that these differences do not hold good in all cases. He
states as a fact that there are Lichens, for the most part crustaceous, such as Secologia ahstrusa, Hymenelia affinis, Sarcogyne
privigna and others, which have no hyphse in their thallus,
although asci and paraphyses are present. Such a fact as this
he considers to be a crushing proof of the absurdity of Schwendener's theory, for here are Lichens in which only one of the
visual constituents is present.
In support of his second proposition he points out that
Baranetzky has observed the protrusion of hyphal filaments from
gonidia, and adds that he has himself seen this occur in Porocyphus and Collema. Such an occurrence is quite unknown
among the true Algse. Furthermore, it is well known that
several forms of gonidia may occur in the same lichen-thallus, as
in Harpidum rutilans, Pannaria granatina, Hacoblenna iremniaca, &c, and Korber suggests that it is extraordinary that a
Lichen should require so many forms of Algee to act as the
gonidia of its thallus. He concludes his argument by saying
that if the gonidia were true Algse they would by this time,
have been all met with in the free state, whereas this is by no
means the case; the gonidia of Nsetrocyinbe, Phylliscum,
Melanormia and others, for instance, have not yet been found
elsewhere than in the lichen-thallus. Moreover, he insists that
when gonidia are found in the free state, they are not therefore
to be regarded as Algse. Finally, he lays stress upon the apparentfact that the gonidia resemble only such so-called Algse as reproduce themselves solely by division.
In supporting the third proposition, the author adopts the
view of Fries, according to which the term " parasitism" is inapplicable in describing the connection of the " fungus" with the
" alga" in a lichen-thallus, and adds that if any " parasitism"
exists at all it must be mutual, pointing out that in a thallus
there are so many gonidia which are not connected with hyphse
that the relation of the latter to the former must be other than
that of a parasite.
In the concluding paragraphs he recalls, as Miiller also does
in his above-mentioned paper, the old view of the origin of the
gonidia from the hyphse, and goes on to say that if the connection of the gonidia with the hyphse is not of a genetic nature, it
must indicate some nutritive process by which the gonidium
obtains from the hypha some of the material which is essential
to its existence. From this stand point he ventures upon some
remarkable speculations as to the probable details of this nutritive process which need not be considered here.
He enumerates finally the various modes in which a lichenthallus may be reproduced, six in all, of which two are by means
RECENT RESEARCHES INTO THE NATURE OF LICHENS.
147
1
of spores, and four by gonidia with (soredia) or without hyphse.
The fact that a lichen-thallus may be developed from cells which
do, as well as from cells which do not, contain chlorophyll establishes, he considers, the autonomy of the Lichens.
Of the publications which afford evidence in favour of Schwendener's theory the first is that of Borzi.2 In it an account
is given of numerous " culture" experiments made with various
Lichens, such as Parmelia puherulenta, Physcia ciliaris, and
others. The conclusions to which the observations led were the
following: (1) that the gonidia stand in no genetic relation to
the hyphffi, but that on the contrary they are autonomous
organisms, true Algse, which serve as hosts for the hyphse;
{%) that the relation between the hyphse and the gonidia is always
such as exists between a Fungus and the substratum upon which
it lives; and (3) that Lichens consist of ascomycetous Fungi
parasitic upon their gonidia, which are true Algse.
An important contribution to the discussion is the paper by
Bornet.3 He begins by giving some account of cases observed
by him in which the gonidia of certain Lichens reassumed their
algal condition. In certain old thalli of OpegrapM varia—the
gonidia of which are furnished by filaments of Trentepohlia
(Chroolepus)—he found that the gonidia had here and there
regained their normal structure. They had become elongated
and had produced numerous sporangia, such as are peculiar to
the genus Trentepohlia, and numerous zoospores could be detected moving amongst them- These fertile filaments were distinctly continuous with those which were still acting as the
gonidia of the Lichen. Again in Pannaria triptophylla, Nyl.
var. nigra, he frequently found projecting from the tubercles of
the tballus which had become ruptured, filaments which were
evidently prolongations of the mass of bluish gonidia contained
in the thallus of this species. These observations convinced him
that the two kinds of gonidia in the thallus of this Lichen,
though so different in appearance, are really two forms of the
same Alga. The filamentous gonidia are but slightly modified
forms, but in the spherical gonidia the original normal algal form
is no longer recognisable.
Further, the thallus of Collema, as is well known, becomes
covered under certain circumstances with great numbers of
small round grains, produced from the extension and development
towards the exterior of a fold of the gonidial filaments. Usually
1
He states that he has observed in Sphserornphale the direct develop
ment
of gonidia from spores (?).
3
'Intorno agli oilici dei gonidi de'Liclieni, Estr. dalla Scienza con ternporanea,
Palermo.' Reprinted in ' Nuov. Qiorn. bot. Ital.,' 1875.
3
"Deuxieme note sur les gonidies des Lichens," 'Ann. Sci. Nat.,' ser.
v, t. x.ix.
148
SYDNEY H. VINES.
hyphae penetrate into this excrescence as it forms, and the result
is that these microscopic grains possess the two structural elements of a Lichen. It occasionally happens, however, as De
Bary1 has shown, that they have no hypbse. They are then simply
Nostocs which entirely resemble those which are to be found
amongst Mosses. Nearly always in such cases the young Nostoc
which is attached to the Collema only by a slight gelatinous
pedicle, becomes detached.
He goes on to cite other examples of the same kind with the
view of proving that the gonidia can easily take on the characters of free Algse and vice-versa. He concludes this part of his
paper by referring to the genus Lichina, expressing an opinion
that the gonidia of this genus are formed by filaments of some
Rivularia, an opinion which was fully borne out by Kny's researches upon the development of the thallus of Lichina p-ygmea?
which were published later in the year.
Having brought so much evidence to prove the identity of the
gonidia of many Lichens with certain of the lower Algae, he
goes on to discuss objections which might be raised against this
view, such an objection, for instance, as that raised by Korber
(see ante), that these Algae are not autonomous organisms but
simply the gonidia of Lichens in a free state. Such an hypothesis, he says, is quite inconsistent with our present knowledge of Algae, for it is certain that these same Algae do not
multiply merely by division, but also by a fructification of their
own which is quite distinct from that of the Lichen. He then
briefly gives an account of various investigations which have been
made into the life-histories of the gonidia, such as Famintziu
and Baranetzky's discovery of zoospores in the Cystococcus
humicola extracted from the thallus of various species of Lichens,
his own observations of the emission of zoospores by Trentepohlia
which furnishes the gonidia of Opegrapha varia, and draws attention to the similarity, amounting to identity according to
Pringsheim, of Phyllactidium which furnishes the gonidial
element of Opegrapka fiUcina, with Cceleochsete.8 Here then
are numerous instances of the multiplication of gonidia by certain specialised reproductive processes, and many instances of the
kind may be cited as occurring amongst those gonidia which
belong to the Phycocbromacse.
He concludes by recounting his experience of separate cultures of gonidia, and of spores of Lichens. The former multiplied immensely but no trace of a hypha could be detected—the
latter germinated and grew, but no gonidia were developed.
1
' Handb. d. Phjs. Bot.,' Bd. ii, Abth. i, p. 290.
3
' Sitzber. d. gesellsch. naturf Freunde in Berlin,' Nov., 1874.
8
See tbis Journal, vol. xv, p. 334.
RECENT RESEARCHES INTO THE NATURE OF LICHENS.
J49
In the 'Counptes Rendus ' for November, 1874, H. A. Weddell draws attention to the Lichinese as being very favorable
objects for observations of this kind. The gonidia not only
form the greater part of the thallus of the Lichens, but they
regulate its form. The hyphse lie in the gelatinous investment
and bear the apothecia. Such Lichens have been termed pseudoalgae. Unfortunately this term has been extended to those
Algae which the opponents of Schwendener's theory regard as
imperfect Lichens, that is, as gonidia; such are Stigoneraa and
Scytonema. If it can be proved that there are true Algse, one
of the strongest objections to the theory would be overthrown.
He considers that such evidence has now been collected. The
researches of Janczewski, and of Thuret and Bornet, upon the
reproduction of Nostoc by spores demolish the argument that it
is an imperfect or a modified form of Collema; and the researches of Bornet (see ante) upon the gonidia of Opegrapha
have the same effect. He then brings forward a communication
made by Gibelli to the Botanical Congress held at Florence
(May, 1874).1 Gibelli had observed the formation of zoospores
in the gonidia of Leeanora subfusca while still in the thallus.
This observation Weddell says enables us to account for the socalled spontaneous appearance of gonidia in parts of the thallus
where none had previously existed. Gibelli also confirms Bornet's
experiments on Opegrapha.
At a meeting of the Societe* Botanique de France, held on
November 27th, the physiological aspects of the question were
discussed. M. Cornu opened the subject by saying that the
peculiar parasitism exhibited by Lichens was not sufficient ground
for separating them from other Ascomycetes. Such a parasitism
exists also in other families of the same group, as, for example,
that of Spharia cupularis upon the red stroma of Nectria
einnabarina, and again, of Asterosporium Hoffmanni upon Cucurbitaria macrospora. M. Weddell pointed out that in these
examples the two organisms belonged to the same family group
of plants, whereas in Lichens it was a cohabitation of organisms
belonging to different classes. The term "parasitism" if used
to describe this cohabitation is used in a forced sense, for the host
instead of suffering grows the more vigorously.
M. Cornuj in reply, referred to the observations of Bornet,
from which it appears that the form of the Algae is somewhat
modified under the influence of thehyphae. M. Weddell rejoined
that in Collema and its allies the hyphae do not come into contact
with the cells of the Nostoc filament, and that, moreover, the
modification of the Alga in other Collemaceae under the influence
of the hyphae is not such as could forbid the assumption that the
• l ' Atti del. cong. intern, bot. Mrenze 1876.'
150
SYDNEY H. VINES.
vegetation of the Alga is under these circumstances more active.
M. van Tieghem distinguished two kinds of parasitism ainoug
Fungi, (1) necessary and (2) voluntary, examples of which lie
adduced in illustration. In Lichens it is otherwise, the cohabitation of Alga and Fungus is a reciprocal parasitism, the Alga
probably supplying the Fungus with carbohydrates and being, in
return, preserved from desiccation by the investing hypbee.
To the number of this Journal for January, 1875, Archer
contributed a paper "On Apothecia in some Scytonematous and
Sirosiphonaoeous Algae in Addition to those Previously Known."
His researches were suggested by those which led Bornet1 to
remove Stigonema atrovirens from the Algse and to place it
among the Lichens under the name of Ephebe pubescent; and
their object was to discover, if possible, in allied forms the distinctly lichenous fructification—apothecia and spermogonia—•
which this species of Stigonema had been found to possess.
Archer was successful in discovering apothecia in Scj/tonema
myochrous, as well as in another unidentified form, in two species
of Svrosiphon {alpinus and pulvinatus), and finally in Stigonema
inamittoswn. He was, therefore, led to assume that these genera
and probably the whole of the Scytonemacese and Sirosiphonacese
could be no longer properly accounted Algse, but should be
relegated with Ephebe to the Lichens. Archer was unable to
detect any hyphse in the species which he examined, though
Schwendener had found them in Ephebe and Bornet in Spilonma
paradoxum and in JJichenosphmria Lenormandi, nor could he
discover any spermogonia.
The next important publication is that of Arcangeli.1 In the
general discussion of the question which precedes the account of
his own researches, he points out that Schwendener's theory has
in its favour the fact that Fungi are parasitic plants incapable of
forming chlorophyll so far as our present knowledge extends.
He argues that it is not, however, impossible to imagine the
existence of plants which, though of a distinctly fungoid nature,
may yet be able to form chlorophyll and to assimilate. Lichens
undoubtedly resemble Fungi very closely both in their vegetative
structure and in their reproductive organs, why then, he asks,
may not Lichens be regarded as plants belonging indeed to the
group of Fungi but containing chlorophyll? In the Phanerogams examples occur of natural families, some members of which
do, and some do not, contain chlorophyll.
He brings forward some observations in support of this view
which tend to prove that chlorophyll may occur in cells of Lichens
1
"Recherches sur la structure de l'Ephebe Pubescens," 'Ann. Sci.
Nat,' s6r. iii, t. xviii.
3
' Sulla questions dei gonidi, Nuov. Giorn. hot. Ttal., 1875.
RECENT RESEARCHES INTO THE NATURE OF LICHENS.
151
other than their gonidia. For instance, he believes that he haa
detected grains of phycochrome in the spores of some Colleinese
and Parmelieae, and a green substance in thehyphse of the thallus
of Pannaria triptophylla.
He regards the researches of Janczewski, of Thuret, and of
Bornet, which give us a knowledge of the complete life-cycle of
Nostoc as affording strong evidence in favour of Schwendener'a
theory, but he does not consider that it suffices to prove the
autonomy of Nostoc. The well-known heteroecious mode of
life of Fungi, as well as their polymorphism, render it quite
probable that such phenomena should also be observed in a
group so nearly allied to them as that of the Lichens.
Then follows an account of various observations of comparatively small importance which tend to prove the similarity of the
tissues of Lichens and Fungi, and of others respecting the
mode of connection between the hypha and the gonidia, which
he has found, in some cases, to be different from that described
by Bornet. With reference to the development of the gonidia
he concludes from his observations upon Usnea barbala, Alectoria
iubata, and Ramalina farinacea, that in the apices of the
branchings of these Lichens gonidia are developed from the
hyphse, for he found them quite isolated in such positions that
their origin could not be referred either to a division of previously existing gonidia or to the entrance of zoospores from
without. He detected a peculiar mode of development iu
Cladonia rangiferina. At the extremities of the branchings of
the thallus he found groups of cells, with ill-defined contours,
in which the hyphse became lost. Near to the apex these
cells are colourless, but farther back they are coloured green
(gonidia), and between these extremes all intermediate stages
occur. The author is inclined to regard these groups of cells as
Soredia.
In many foliaceous and crustaceons Lichens, such as Nepkroma levigatum, Sticta pulmonacea, Peltigera canina, and others,
he detected another mode of development of gonidia. All these
Lichens are invested either on one or on both surfaces by a
cortical layer of pseudo-parenchyma. A gradual transition can
be made out between the colourless cells of this tissue and
others, lying internally, with completely green cell-contents
(gonidia).
In Pannaria triptophylla the author also detected some instructive peculiarities. He found that the tubercles on the
surface of the thallus at an early stage contained only one gonidium, or at most a very few, and in this condition they resemble
Nostoc-cells or filaments. When these tubercles are mature
they usually are ruptured and through the opening filaments of
152
SYDNEY H. VINES.
gonidia protrude which have a basal heterocyst, and closely resemble filaments of Eivularia. These observations agree in the
main with those of Boruet already mentioned. The author
describes the development of these tubercles as taking place in
two ways; in the one, they are formed by a coalescence of the
hyphse of the thallus to form a group of cells in the manner
already described in speaking of the development of gonidia in
Cladonia rangiferina, in the other, they are formed from soredia
derived from older tubercles which became invested by hyphse.
The mode of origin of the gonidia in the tubercles is similar to
that which takes place in the cortex. From these facts, and
from the occurrence of numerous gradational forms both as to
shape and as to colour, it appears that the gonidia of this Lichen
are in reality all of one kind, a conclusion at which Bornet had
also arrived.
Finally, the author points out the improbability of the views
held by van Tieghein and by Weddell as to the existence of
parasitism in Lichens. He considers that the gonidia do not
arise from spores which have recently germinated, but from organs
which have a more or less pseudo-parenchymatous structure, a
view which finds support in the facts above detailed. He concludes that various Protococcacese, Nostocacese, and Rivulariacese
are only certain forms of lichen-gonidia in certain phases of
their vegetation, and that therefore the gonidia are organs peculiar to Lichens.
In the ' Flora' for that year, Winter1 published a paper in
which he shews that four of the examples adduced by Ko'rber
(see ante), in support of his statement that Lichens exisis which
possess no hyphse, viz., Secologia abstrusa, Sarcogyne privigna,
Hymenelia, affinis and Nmtrocymbe faliginea, 8do, as a matter of
fact, possess hjphee. In a second publication, he exposes the
inaccuracy of Korber's statements with regard to Spheeromphale
and its allies, (1) in that hyphae do actually exist in this Lichen,
and f 2) in that the spores on germinating do form hyphse and do
not, as Korber asserts, give rise directly to gonidia. These
observations suffice to answer some of the more important objections—because based apparently upon experimental evidence—
brought forward by Korber against Schwendener's theory.
'Nature' for January 27, 1876, contains a commmunication
from Lauder Lindsay upon the nature of Lichens. In it he
criticises severely the views of Schwendener and his followers,
and repeats his suggestion for the establishment of intermediate
and provisional groups of Algo-lichenes and Fungo-lichenes. He
1
' Zur Anatomie der Kriistenflecliten.'
5
' Ueber die Gattung Sphaeroraphale und Verwandte, Prings, Jahrb. f.
Wiss. Bot.,' Bd. x.
RECENT RESEARCHES INTO THE NATURE OF LICHENS.
153
points out that there are several difficulties in the natural history
of Lichens with which the Schwendenerians have to deal, as, for
instance, the case of Athalline Lichens that have neither hyphse
nor gonidia, that are represented, in fact, only by apothecia—
and for examples he refers to Archer's paper which has been considered above. It must be remarked that the author appears
to have overlooked the conclusions at which Archer arrived.
He finishes his letter by comparing Schwendener with Bayrhoffer!
An interesting paper was contributed later on in the year by
T^rank.1 As the result of his observations on the development
of the gonidia he states that there two ways in which they are
formed in the lichen-thallus ; (1) usually they are derived from
those already existing in the thallus; (£) they make their way
into the growing thallus from without, and then multiply.
Another mode of
origin of gonidia was described about the same
time by Minks.2 According to his observations the germinating
spore gives rise to a mass of hyaline hyphse from which, together
with the coloured secondary hypha (which is probably connected
with the development of the apothecia) certain organs are formed,
—termed by him Gonangia and Gonocystia—within which
gonidia are formed by free-cell formation.
In passing to the consideration of the papers published in 1877
upon this subject it is interesting to recall a sentence which
occurs in Lauder Lindsay's letter, already quoted. He says : " If,
by artificial cultivation, such a union {i.e., of Fungus and Alga)
could be made to produce a Lichen, the theory might
he held as
proven." Such evidence is afforded by Stahl's3 paper on the
nature of hymenial gonidia, as the following account will
show.
The experiments which had previously been made in this direction by Reess, Bornet and Treub, had met with only partial
success. In all cases the lichen-spores after being sown upon
various Algae germinated, and their hyphse formed with the Algae,
a structure resembling in some degree the thallus of a Lichen,
but in no case was any fructification ever developed. Stahl's
researches upon the hymenial gonidia enabled him to overcome
the difficulties which had marred the success of the experiments ,
of his predecessors, and enabled him to trace the whole course^
1
' Ueb. d. biolog. Verhaltnisse des Thallus einiger Kriistenflechten,
Cohn's
Beitrage,' Bd. ii.
2
'Beit. z. Kennt. des Baues und Lebens der Flechten, ], Gonangium
und Gonocystium,' Wien, 1876.
» ' Beitrage zurEntwickelungs-geschichte der Flechten, 1877.' 1. "Ueber
die geschlechtliclie Fortpflanzung der Collemaceen." 2. "Ueberdie Bcdeutung der Hymenial-gonidicn." The first of these papers will be discussed at another time.
154
SYDNEY H. VINES.
of the development of the lichen-thallus from the germination
of the spore to the formation of apothecia.
These hymenial gonidia are, as their name denotes, gonidia
which occur in the hymenial layer of the apothecium in certain
Lichens. Nylander seems to have been the first to observe them,
and the subsequent investigations of Fuisting and of Winter,
have shewn that they originate from the ordinary gonidia of the
thallus. They differ from the gonidia of the thallus in that they
are smaller and are of a less vivid colour. The primary object
of Stahl's researches was to account for this difference in appearbetween these two kinds of gonidia, and to discover the real
significance of the presence of gonidia in the hymenium.
The Lichen which he more especially studied was Endocarpon
pusillum (Hedwig). In its thallus the gonidia, which are of a
uniform green colour, form a layer lying between the medullary
and cortical parts and extending here and there for a greater or
less distance into the cortex. By their mode of division they
indicate their connection with the algal genus Pleurococcus. The
perithecia present the structure which is usually found in pyrenocarpous Lichens. In the spaces between the asci (Fig. 1), and more
or lessfillingup its whole cavity, is a gelatinous substance which is
produced by the swelling up of the membranes of emptied asci,
in which lie the numerous pale-green hymenial gonidia. They
differ remarkably in size from the gonidia of the thallus, having
a diameter of only O'OOii—0"004 m.tn., whereas the diameter of
the latter is from 0'008—O'OISJ m.m. Each ascus usually contains two spores of unequal size, the upper one being rather
larger than the lower. When ripe, they are brown, multicellular,
pseudo-parenchymatous structures of considerable size. When
moistened, the asci and the gelatinous substance surrounding
them absorb a quantity of water and swell-up. In consequence
of the tension thus produced within the perithecium, the ripe
asci burst and expel their spores with such force that they are
projected to a distance of several centimeters.
An examination of the spores which have been thus extruded
shews that they are surrounded by a number of the pale-green
hymenial gonidia. (Fig. 2). If a spore be kept moist, it germinates at once after its extrusion, and if it be placed upon a glass
slide the whole process can be easily observed. A certain number
of the hyphse which spring from the segments of the spore
invest the hymenial gonidia by which the spores is surrounded
(Fig. 3), and in a few days the invested gonidia shew that they
have undergone considerable change. The previously scanty
chlorophyll which gave them a pale-green colour has increased in
quantity, so that the enlarged gonidia are uniformly dark-green.
A comparison of the free and of the enclosed gonidia shewn in
RECENT RESEARCHES INTO THE NATURE OF LICHENS.
155
fig. 3, cannot fail to suggest that the increase in size exhibited by
the latter must be attributed to the influence of the Fungus.
They have ceased to undergo division, whereas the free gonidia
have given rise to numerous individuals. Other hyphse grow and
ramify, and although they come here and there into contact with
gonidia, they do not grow round them, but continue to grow in
a straight line along the surface of the slide. These hyphse correspond to those which, on a normal substratum (rhizines) penetrate into it and act as absorbing organs.
The cultures of Endocarpon made in this way, although the
plants continued to live for as long as six months, were never so
successful as to produce a thallus distinctly differentiated into
cortical and medullary portions; apparently the conditions were
altogether too abnormal. An endeavour was made to make the
conditions more favourable by substituting for the glass-slide, as
a substratum, a piece of porous earthenware, the cavities of which
had been filled up with soil deposited from suspension in water.
Under these circumstance the young thallus presents at an early
stage a differentiation into an upper portion which contains the
gonidia, and a lower which is subterranean. (Figs. 4 and 5).
The structure of the upper portion is at first very simple, consisting of a mass of closely-packed gonidia and hyphse invested by
a layer of pseudo-parenchyma, but gradually a differentiation
into a cortical and a medullary part, with an intervening gonidial
layer, becomes apparent.
The lower, subterranean portion
(hypothallus) consists of colourless, septate, branched and anastomosing hyphse, some of which are isolated and others are
aggregated in bundles.
Soon after this stage of development has been attained the
first Spermogonia make their appearance. They are ovoid in form
and are completely sunk in the thallus; they contain no gonidia.
The first appeared within six weeks after the sowing of the spores,
and very shortly afterwards the first formation of perithecia became evident. The first spores came to maturity within four or
five months.
The history of the hymenial gonidia which did not become
invested by hyphse affords some interesting facts. It has already
been mentioned that they divide, and that the products of their
division do not exceed in size the mother-cells from which they are
derived. The divisions take place in one direction only, namely,
at right angles to the longer axis of the cells, so that the Alga
ought to be considered in this condition to belong to Naegeh's
genus Stichococcus, were it not that further observations shew
•that these two genera must be united.
Prank has suggested that possibly the gonidia, in consequence
of having been for many generations so intimately associated with
156
SYDNEY H. VINES.
hyphse, have become incapable of active independent vegetation—
Stahl does not consider that the facts justify such a view. It is
true that the size of the algal cells which are left to vegetate
freely is, on an average, much smaller than that of the cells
which are acting as gonidia; but the rapid reproduction of the
freely vegetating Alga cannot co-exist with imperfect nutrition.
The differences in size and appearance must probably be attributed solely to the various mechanical or physical conditions to
which the Alg8e are respectively exposed.
Observations of a similar nature were made on Thelidium
minululum (Korber). This Lichen made its appearance regularly in the cultures of Endocarpon. It could not have made its
way thither by means of soredia, and the only means of accounting for its appearance is the assumption that it was produced
from spores which, on germinating, availed themselves of some
of the extruded hymenial gonidia of Endocarpon to form a
thallus. This assumption was proved true by direct experiment.
The spores of Thelidium sown in the absence of gonidia gave
rise to a mycelium which, so soon as the store of nutriment contained in the spore was exhausted, withered away ; but if sown
with gonidia of Endocarpon a fructifying thallus was gradually
formed. In this case also the influence of the Fungus upon the
Alga was made apparent by the increased size of the latter, and
in the larger amount of chlorophyll contained within it.
Further interesting facts were obtained by the investigation of
Polyblastia rugulosa (Massal.). The spaces between the asci of
this Lichen (each of which contains usually eight spores) are occupied by hymenial gonidia arranged in rows, derived originally from
the gonidia of the thallus—from which they differ in a very
marked manner, the former being rod-like, the latter more or less
rounded and dividing like the pleurococcoid gonidia of Endocarpon. If some of the thallus gonidia be cultivated on a slide
they will be seen to divide in successive planes in the three
dimensions of space. The products of this division are not,
however, rounded cells like those from which they are formed,
but are cylindrical and divide only in a plane at right angles to
their length, the segments separating the one from the other.
Thus it is possible to obtain from gonidia dividing like PJeurococcus the algal form known as Stichococcus. This Stichococcus
is identical in form, in size, and in the mode of its division with
the rod-shaped gonidia occurring in the hyinenium.
As in Endocarpon so in Polyblastia, a certain number of
hymenial gonidia are extruded from the peritheciura together with
the spore, which became invested by hyphse when the spore germinates. The rod-shaped hymenial gonidia then gradually lose
their cylindrical form, increase in size and assume the rounded
RECENT RESEARCHES INTO THE NATURE OF LICHENS. 157
contour which characterises the gonidia of the thallus of the
Lichen in question.
The conclusions arrived at as the result of the foregoing investigations are as follows :—(1) in those Lichens which possess
hymenial gonidia the thallus is regularly produced by the coming
together of the spore of the ascomycetous Fungus and the Alga;
(2) the hymenial gonidia when actively dividing derive their
nutriment from the constituents of the structure in which they
are enclosed : in view of the small quantity of chlorophyll
which they contain, it does not seem probable that they give up
to the Ascomycete any of the products of their assimilation;
(3) if it be suggested that the hymenial gonidia appear to resemble the entophytic algal colonies found in Anthoceros, Azolla,
Gunnera and others, it must be remembered that they are of
extreme physiological importance in the economy of the Lichen
in that they afford to the germinating spores material for the
formation of a new thallus.
With this account of Stahl's observations this resume" of the
lichen-gonidia discussion must for the present close. It is quite
evident that the theory of the structure of Lichens which was
suggested originally by De Bary and first tested experimentally
by Schwendener is gradually becoming established upon a sure
foundation of accurate observations. It will be noticed that the
objections brought against it are, on the whole, more of a theoretical than of a practical nature. The theoretical objections
may be regarded as silenced by the researches above alluded to
of Winter, Prank and Stahl, and if further experimental evidence
be required it is to be found in Stahl's paper on the sexual reproduction of the Collemacese, which will be discussed hereafter.
The practical objections are mainly the observations of Arcangeli
and of Minks, which seem to shew that gonidia may be developed from hyphse. It must be remarked that although these
observations tend to prove the same fact, yet they differ widely,
and therefore cannot be regarded as being confirmatory the one
of the other. It remains to be seen whether or not other observers will in the future be successful in repeating these observations, and if they will endorse the interpretations which have been
put upon them.
VOL. XVin.—-NEW SER.