Chapter XV: Front Matter (15)

_Gonidia._--It has been made clear above that the gonidia are nothing more than algal cells, which have been ensnared by fungal hyphae and made to develop in captivity (fig. 1). Funfstuck gives ten free living algae which have been identified as the gonidia of lichens. _Pleurococcus_ (_Cystococcus_) _humicola_ in the majority of lichens, e.g. _Usnea_, _Cladonia_, _Physcia_, _Parmelia_, _Calicium_, many species of _Lecidea_, &c., _Trentepohlia_ (_Chroolepus_) _umbrina_ in many species of _Verrucaria_, _Graphidieae_ and _Lecidea_; _Palmella botryoides_ in _Epigloea_; _Pleurococcus vulgaris_ in Acarospora, Dermatocarpon, Catillaria; _Dactylococcus infusionum_ in _Solorina_, _Nephromia_; _Nostoc lichenoides_ in most of the Collemaceae; _Rivularia rutida_ in _Omphalaria_; _Lichina_, &c., _Polycoccus punctiformis_ in _Peltigera_, _Pannaria_ and _Stictina_; _Gloeocapsa polydermatica_ in _Baeomyces_ and _Omphalaria_; _Sirosiphon pulvinatus_ in _Ephebe pubescens_. The majority of lichens are confined to one particular kind of gonidium (i.e. species of alga) but a few forms are known (_Lecanora granatina_, _Solorina crocea_) which make use of more than one kind in their development. In the case of _Solorina_, for example, the principal alga is a green alga, one of the Palmellaceae, but _Nostoc_ (a blue-green alga) is also found playing a subsidiary part as gonidia. In L. _granatina_ the primary alga is _Pleurococcus_, the secondary, _Gleococapsa_.

FIG. 5.--_Usnea barbata_. (Nat. size.) _ap_, Apothecium.]

_Cephalodia._--In about 100 species of lichens peculiar growths are
developed in the interior of the thallus which cause a slight
projection of the upper or lower surface. These structures are known
as _cephalodia_ and they usually occupy a definite position in the
thallus. They are distinguished by possessing as gonidia algae foreign
to the ordinary part of the thallus. The foreign algae are always
members of the Cyanophyceae and on the same individual and even in the
same cephalodium more than one type of gonidium may be found. The
function of these peculiar structures is unknown. Zukal has suggested
that they may play the part of water-absorbing organs.

The exact relation of gonidia and hyphae has been investigated especially by Bornet and also by Hedlund, and very considerable differences have been shown to exist in different genera. In _Physma_, _Arnoldia_, _Phylliscum_ and other genera the gonidia are killed sooner or later by special hyphal branches, _haustoria_, which pierce the membrane of the algal cell, penetrate the protoplasm and absorb the contents (fig. 11, C). In other cases, e.g. _Synalissa_, _Micarea_, the haustoria pierce the membrane, but do not penetrate the protoplasm (fig. 11, D). In many other cases, especially those algae possessing _Pleurococcus_ as their gonidia, there are no penetrating hyphae, but merely special short hyphal branches which are in close contact with the membrane of the algal cell (fig. 3).

FIG. 6.--_Cladonia rangiferina_. (Nat. size.)

A, Sterile.
B, With ascus-fruit at the ends of the branches.]

FIG. 7.--_Cladonia coccifera_. Podetia bearing apothecia. (Nat. size.)

_t_, Scales of primary thallus.]

_Reproduction_.

There are three methods of reproduction of the lichen: by fragmentation, by soredia, by the formation of fungal spores. In the first process, portions of thallus containing gonidia may be accidentally separated and so may start new plants. The second method is only a special process of fragmentation. The soredia are found in a large number of lichens, and consist of a single gonidium or groups of gonidia, surrounded by a sheath and hyphae. They arise usually in the gonidial layer of the thallus by division of the gonidia and the development around them of the hyphal investment; their increase in number leads to the rupture of the enclosing cortical layer and the soredia escape from the thallus as a powdery mass (fig. 12). Since they are provided with both fungal and algal elements, they are able to develop directly, under suitable conditions, into a new thallus. The soredia are the most successful method of reproduction in lichens, for not only are some forms nearly always without spore-formation and in others the spores largely abortive, but in all cases the spore represents only the fungal component of the thallus, and its success in the development of a new lichen-thallus depends on the chance meeting, at the time of germination, with the appropriate algal component.

_Conidia._--Contrary to the behaviour of the non-lichen forming
Ascomycetes the lichen-fungi show very few cases of ordinary conidial
formation. Bornet describes free conidia in _Arnoldia minitula_, and
_Placodium decipiens_ and _Conidia_-formation has been described by
Neubner in the Caliciae.

FIG. 8.--Usnea barbata. (Mag. nearly 100 times.)

A, Optical longitudinal section of the extremity of a thin branch of
the thallus which has become transparent in solution of potash.
B, Transverse section through a stronger branch with the point of
origin of an adventitious branch (sa).
r, Cortical layer.
m, Medullary layer.
x, Stout axile strand.
g, The algal zone (_Cystococcus_).
s, Apex of the branch.]

_Spermatia._--In the majority of genera of lichens small flask-shaped
structures are found embedded in the thallus (fig. 13). These were
investigated by Tulasne in 1853, who gave them the name _spermogonia_
The lower, ventral portion of the spermogonium is lined by delicate
hyphae, the _sterigmata_, which give origin to minute colourless
cells, the _spermatia_. The sterigmata are either simple (fig. 13, C)
or septate--the so-called arthrosterigmata (fig. 13, B). The
spermogonia open by a small pore at the apex, towards which the
sterigmata converge and through which the spermatia escape (fig. 13).
There are two views as to the nature of the spermatia. In one view
they are mere asexual conidia, and the term _pycnoconidia_ is
accordingly applied since they are borne in structures like the
non-sexual _pycnidia_ of other fungi. In the other view the spermatia
are the male sexual cells and thus are rightly named; it should,
however, be pointed out that this was not the view of Tulasne, though
we owe to him the designation which carries with it the sexual
significance. The question is one very difficult to settle owing to
the fact that the majority of spermatia appear to be functionless. In
favour of the conidial view is the fact that in the case of _Collema_
and a few other forms the spermatia have been made to germinate in
artificial cultures, and in the case of _Calicium parietinum_ Möfler
succeeded in producing a spermogonia bearing thallus from a
spermatium. For the germination of the spermatia in nature there is
only the observation of Hedlund, that in _Catillaria denigrata_ and
_C. prasena_ a thallus may be derived from the spermatia under natural
conditions. In relation to the view that the spermatia are sexual
cells, or at least were primitively so, it must be pointed out that
although the actual fusion of the spermatial nucleus with a female
nucleus has not been observed, yet in a few cases the spermatia have
been seen to fuse with a projecting portion (trichogyne) of the
ascogonium, as in _Collema_ and _Physcia_, and there is very strong
circumstantial evidence that fertilization takes place (see later in
section on development of ascocarp). The resemblance of the spermatia
and spermogonia to those of Uredineae should be pointed out, where
also there is considerable evidence for their original sexual nature,
though they appear in that group to be functionless in all cases. The
observations of Möller, &c., on the germination cannot be assumed to
negative the sexual hypothesis for the sexual cells of _Ulothrix_ and
_Ectocarpus_, for example are able to develop with or without fusion.
The most satisfactory view in the present state of our knowledge seems
to be that the spermatia are male cells which, while retaining their
fertilizing action in a few cases are now mainly functionless. The
female sexual organs, the ascogonia, would thus in the majority of
cases develop by the aid of some reduced sexual process or the
ascocarps be developed without relation to sexual organs. A further
argument in support of this view is that it is in complete agreement
with what we know of the sexuality of the ordinary, free-living
ascomycetes, where we find both normal and reduced forms (see FUNGI).

FIG. 9.--Section of Heteromerous Lichen Thallus.

a, Upper cortical layer.
d, Lower cortical layer.
c, Medullary layer.
b, Gonidial layer.]

FIG. 11.--Lichen-forming Algae. (A, C, D, E mag. 950, B 650 times.)
The alga is in all cases indicated by the letter _g_, the assailing
hyphae by _h_.

A, _Pleurococcus_, Ag. (_Cystococcus_, Näg.) attacked by the germ-tube
from a spore of _Physica parietina_.
B, _Scytonema_ from the thallus of _Stereocaulon famulosum_.
C, _Nostoc_ from the thallus of _Physma chalazanum_.
D, _Gloeocapsa_ from the thallus of _Synalissa Symphorea_.
E, _Pleurococcus_ Sp. (_Cystococcus_) from the thallus of _Cladonia
furcata_.]

_Fruit Bodies._--We find two chief types of fruit bodies in the lichens, the _perithecium_ and _apothecium_; the first when the fungal element is a member of the Pyrenomycetes division of the Ascomycetes, the second when the fungus belongs to the Discomycetes division. In the two genera of lichens--the _Basidiolichens_--in which the fungus is a member of the Basidiomycetes, we have the fructification characteristic of that class of fungi: these are dealt with separately. The perithecium is very constant in form and since the gonidia take no part in the formation of this organ or that of the apothecium it has the general structure characteristic of that division of fungi. The apothecia, though of the normal fungal type and usually disk-shaped, are somewhat more variable, and since the variations are of value in classification some more details may be added.

FIG. 12.--_Usnea barbata._ (Mag. more than 500 times.)

c, An isolated mature soredium, with an algal cell (_Pleurococcus_) in
the envelope or hyphae.
d, Another with several algal cells in optical longitudinal section.
e, f, Two soredia in the act of germinating; the hyphal envelope has
grown out below into rhizoid branches, and above shows already the
structure of the apex of the thallus (see fig 9).]

They present various shapes, of which the following are the principal:
(a) _peltate_, which are large, rounded, without any distinct thalline
margin[1] (e.g. _Usnea_, _Peltigera_); (b) _lecanorine_, or
scutelliform, which are orbicular and surrounded by a distinct, more
or less prominent thalline margin (e.g. _Parmelia_, _Lecanora_),
having sometimes also in addition a proper one¹ (e.g. _Thelotrema_,
_Urceolaria_); (c) _lecideine_, or patelliform, which are typically
orbicular, with only a proper margin (e.g. _Lecidea_), sometimes
obsolete, and which are occasionally irregular in shape, angular or
flexuose (e.g. _Lecidea jurana_, _L. myrmecina_), or complicated and
gyrose (e.g. _Gyrophora_), and even stipitate (e.g. _Baeomyces_); (d)
_lirelliform_, which are of very irregular figure, elongated, branched
or flexuose, with only a proper margin (e.g. _Xylographa_, _Graphis_,
&c.) or none (e.g. some _Arthoniae_), and often very variable even in
the same species. In colour the apothecia are extremely variable, and
it is but rarely that they are the same colour as the thallus (e.g.
_Usnea_, _Ramalina_). Usually they are of a different colour, and may
be black, brown, yellowish, or also less frequently rose-coloured,
rusty-red, orange-reddish, saffron, or of various intermediate shades.
Occasionally in the same species their colour is very variable (e.g.
_Lecanora metaboloides_, _Lecidea decolorans_), while sometimes they
are white or glaucous, rarely greenish, pruinose. Lecideine apothecia,
which are not black, but otherwise variously coloured, are termed
_biatorine_.

FIG. 13.--A, B, _Gyrophora cylindrica._ (A mag. 90, B 390 times, C
highly magnified.)

A, A vertical median section through a spermogonium imbedded in the
thallus.
o, Upper rind.
u, Under rind.
m, Medullary layer of the thallus.
B, Portion of a very thin section from the base of the spermogonium.
w, Its wall from which proceed sterigmata with rod-like spermatia
(s).
m, Medullary hyphae of the thallus.
C, _Cladonia novae Angliae_, Delise; sterigmata with spermatia from
the spermogonium.]

The two principal parts of which an apothecium consists are the
_hypothecium_ and the hymenium, or thecium. The _hypothecium_ is the
basal part of the apothecium on which the _hymenium_ is borne; the
latter consists of asci (thecae) with ascospores, and paraphyses. The
paraphyses (which may be absent entirely in the Pyrenolichens) are
erect, colourless filaments which are usually dilated and coloured at
the apex; the apices are usually cemented together into a definite
layer, the _epithecium_ (fig. 14). The spores themselves may be
unicellular without a septum or multicellular with one or more septa.
Sometimes the two cavities are restricted to the two ends of the
spore, the _polari-bilocular_ type and the two loculi may be united
by a narrow channel (fig. 15). At other times the spores are divided
by both transverse and longitudinal septa producing the muriform
(murali-divided) spore so called from the resemblance of the
individual chambers to the stones in a wall. The very large single
spores of _Pertusaria_ have been shown to contain numerous nuclei and
when they germinate develop a large number of germ tubes.

FIG. 14.--Diagram showing Apothecium in Section and surrounding
Portion of Thallus, and special terms used to designate these
parts.]

_Development of the Ascocarps._--As the remarks on the nature of the
spermatia show, the question of the sexuality of the lichens has been
hotly disputed in common with that of the rest of the Ascomycetes. As
indicated above, the weight of evidence seems to favour what has been
put forward in the case of the non-lichen-forming fungi (see FUNGI),
that in some cases the ascogonia develop as a result of a previous
fertilization by spermatia, in other cases the ascogonia develop
without such a union, while in still other cases the reduction goes
still farther and the ascogenous hyphae instead of developing from the
ascogonia are derived directly from the vegetative hyphae.

a, Paraphyses.
b, Asci (thecae) with bilocular spores.
c, Hypothecium.]

The first exact knowledge as to the origin of the ascocarp was the
work of Stahl on _Collema_ in 1877. He showed that the archicarp
consisted of two parts, a lower coiled portion, the ascogonium, and an
upper portion, the trichogyne, which projected from the thallus. Only
when a spermatium was found attached to the trichogyne did the further
development of the ascogonium take place. From these observations he
drew the natural conclusion that the spermatium was a male, sexual
cell. This view was hotly contested by many workers and it was sought
to explain the trichogyne--without much success--as a respiratory
organ, or as a boring organ which made a way for the developing
apothecium. It was not till 1898, however, that Stahl's work received
confirmation and addition at the hands of Baur (fig. 16). The latter
showed that in _Collema crispum_ there are two kinds of thalli, one
with numerous apothecia, the other quite sterile or bearing only a
few. The sterile thalli possessed no spermogonia, but were found to
show sometimes as many as 1000 archicarps with trichogynes; yet none
or very few came to maturity. The fertile thalli were shown to bear
either spermogonia or to be in immediate connexion with
spermogonia-bearing thalli. Furthermore Baur showed that after the
fusion of the spermatium with the trichogyne the transverse walls of
that organ became perforated. There was thus very strong
circumstantial evidence in favour of fertilization, although the male
nucleus was not traced. The further work of Baur, and that of
Darbishire, Funfstuck and Lindau, have shown that in a number of other
cases trichogynes are present. Thus ascogonia with trichogynes have
been observed in _Endocarpon_, _Collema_, _Pertusaria_, _Lecanora_,
_Gyrophora_, _Parmelia_, _Ramalina_, _Physcia_, _Anaptychia_ and
_Cladonia_. In _Nephroma_, _Peltigera_, _Peltidea_ and _Solorina_ a
cogonia without trichogynes have been observed. In _Collema_ and a
form like _Xanthoria parietina_ it is probable that actual
fertilization takes place, and possibly also in some of the other
forms. It is probable, however, that in the majority of cases the
ascogonia develop without normal fertilization, as is necessarily the
case where the ascogonia have no trichogynes or the spermatia are
absent. In these cases we should expect to find some reduced process
of fertilization similar to that of _Humaria granulata_ among the
ordinary Ascomycetes, where in the absence of the antheridia the
female nuclei fuse in pairs. In other lichens we should expect to find
the ascogenous hyphae arising directly from the vegetative hyphae as
in _Humaria rutilans_ among the ordinary fungi, where the process is
associated with the fusion of vegetative nuclei. It is possible that
_Solorina saccata_ belongs to this class. Cytological details of
nuclear behaviour among the lichens are, however, difficult to obtain
owing to the slow growth of these forms and the often refractory
nature of the material in the matter of preparation for microscopical
examination.

FIG. 16.--_Collema crispum._

A, Carpogonium, c, with its trichogyne t.
B, Apex of the trichogyne with the spermatium, s, attached.]

_Ejection of Spores._--The spores are ejected from the apothecia and
perithecia as in the fungi by forcible ejaculation from the asci. In
the majority of forms it is clear that the soredia rather than the
ascospore must play the more important part in lichen distribution as
the development of the ordinary spores is dependent on their finding
the proper alga on the substratum on which they happen to fall. In a
number of forms (_Endocarpon pusillum_, _Stigmaatonima cataleptum_,
various species of _Staurothele_), however, there is a special
arrangement by which the spores are, on ejection, associated with
gonidia. In these forms gonidia are found in connexion with the young
fruit; such algal cells undergo numerous divisions becoming very small
in size and penetrating into the hymenium among the asci and
paraphyses. When the spores are thrown out some of these hymenial
gonidia, as they are called, are carried with them. When the spores
germinate the germ-tubes surround the algal cells, which now increase
in size and become the normal gonidia of the thallus.

_Basidiolichens._

FIG. 17.--_Cora pavonia._ A, Viewed from above; B, From below; _hym_,
hymenium. (Nat. size.)]

As is clear from the above, nearly all the lichens are produced by the association of an ascomycetous fungus with algae. For some obscure reason the Basidiomycetes do not readily form lichens, so that only a few forms are known in which the fungal element is a member of this family. The two best-known genera are _Cora_ and _Dictyonema_; _Corella_, whose hymenium is unknown, is also placed here by Wainio. The so-called Gasterolichens, _Trichocoma_ and _Emericella_, have been shown to be merely ascomycetous fungi. _Clavaria mucida_, however, has apparently some claims to be considered as a Basidiolichen, since the base of the fruit body and the thallus from which it arises, according to Coker, always shows a mixture of hyphae and algae.

The best-known species is _Cora pavonia_, which is found in tropical regions growing on the bare earth and on trees; the gonidia belong to the genus _Chroococcus_ while the fungus belongs, apparently, to the Thelephoreae (see FUNGI). This lichen seems unique in the fact that the fungal element is also found growing and fruiting entirely devoid of algae, while in the ascolichens the fungus portion seems to have become so specialized to its symbiotic mode of life that it is never found growing independently.

The genus _Dictyonema_ has gonidia belonging to the blue-green alga, _Scytonema_. When the fungus predominates in the thallus it has a bracket-like mode of growth and is found projecting from the branches of trees with the hymenium on the under side. When the alga is predominant it forms felted patches on the bark of trees, the _Laudatea_ form. It is said that the fungus of _Cora pavonia_ and of _Dictyonema_ is identical, the difference being in the nature of the alga.

_Mode of Life._

Lichens are found growing in various situations such as bare earth, the bark of trees, dead wood, the surface of stones and rocks, where they have little competition to fear from ordinary plants. As is well known, the lichens are often found in the most exposed and arid situations; in the extreme polar regions these plants are practically the only vegetable forms of life. They owe their capacity to live under the most inhospitable conditions to the dual nature of the organism, and to their capacity to withstand extremes of heat, cold and drought without destruction. On a bare rocky surface a fungus would die from want of organic substance and an alga from drought and want of mineral substances. The lichen, however, is able to grow as the alga supplies organic food material and the fungus has developed a battery of acids (see below) which enable it actually to dissolve the most resistant rocks. It is owing to the power of disintegrating by both mechanical and chemical means the rocks on which they are growing that lichens play such an important part in soil-production. The resistance of lichens is extraordinary; they may be cooled to very low temperatures and heated to high temperatures without being killed. They may be dried so thoroughly that they can easily be reduced to powder yet their vitality is not destroyed but only suspended; on being supplied with water they absorb it rapidly by their general surface and renew their activity. The life of many lichens thus consists of alternating periods of activity when moisture is plentiful, and completely suspended animation under conditions of dryness. Though so little sensitive to drought and extremes of temperature lichens appear to be very easily affected by the presence in the air of noxious substances such as are found in large cities or manufacturing towns. In such districts lichen vegetation is entirely or almost entirely absent. The growth of lichens is extremely slow and many of them take years before they arrive at a spore-bearing stage. _Xanthoria parietina_ has been known to grow for forty-five years before bearing apothecia. This slowness of growth is associated with great length of life and it is probable that individuals found growing on hard mountain rocks or on the trunks of aged trees are many hundreds of years old. It is possible that specimens of such long-lived species as _Lecidea geographica_ actually outrival in longevity the oldest trees.

_Relation of Fungus and Alga._

The relation of the two constituents of the lichen have been briefly stated in the beginning of this article. The relation of the fungus to the alga, though it may be described in general terms as one of symbiosis, partakes also somewhat of the nature of parasitism. The algal cells are usually controlled in their growth by the hyphae and are prevented from forming zoospores, and in some cases, as already described, the algal cells are killed sooner or later by the fungus. The fungus seems, on the other hand, to stimulate the algal cells to special development, for those in the lichen are larger than those in the free state, but this is not necessarily adverse to the idea of parasitism, for it is well known that an increase in the size of the cells of the host is often the result of the attacks of parasitic fungi. It must be borne in mind that the exact nutritive relations of the two constituents of the lichen have not been completely elucidated, and that it is very difficult to draw the line between symbiosis and parasitism. The lichen algae are not alone in their specialization to the symbiotic (or parasitic) mode of life, for, as stated earlier, the fungus appear in the majority of cases to have completely lost the power of independent development since with very rare exceptions they are not found alone. They also differ very markedly from free living fungi in their chemical reactions.

_Chemistry of Lichens._

The chemistry of lichens is very complex, not yet fully investigated
and can only be very briefly dealt with here. The wall of the hyphae
of the fungus give in the young state the ordinary reactions of
cellulose but older material shows somewhat different reactions,
similar to those of the so-called fungus-cellulose. In many
lichen-fungi the wall shows various chemical modifications. In
numerous lichens, e.g. _Cetraria islandica_, the wall contains
Lichenin (C6H10O5), a gummy substance which swells in cold water and
dissolves in hot. Besides this substance, a very similar one,
Isolichenin, is also found which is distinguished from lichenin by the
fact that it dissolves in cold water and turns blue under the reaction
of Iodine. Calcium oxalate is a very common substance, especially in
crustaceous lichens; fatty oil in the form of drops or as an
infiltration in the membrane is also common; it sometimes occurs in
special cells and in extreme cases may represent 90% of the dry
substance as in _Verrucaria calciseda_, _Biatora immersa_.

_Colouring Matters._--Many lichens, as is well known, exhibit a vivid
colouring which is usually due to the incrustation of the hyphae with
crystalline excretory products. These excretory products have usually
an acid nature and hence are generally known as lichen-acids. A large
number of these acids, which are mostly benzene derivatives, have been
isolated and more or less closely investigated. They are characterized
by their insolubility or very slight solubility in water; as examples
may be mentioned erythrinic acid in _Roccella_ and _Lecanora_; evernic
acid in species of _Evernia_, _Ramalina_ and _Cladonia_; lecanoric
acid in _Lecanora_, _Gyrophora_. The so-called chrysophanic acid found
in _Xanthoria_ (Physcia) _parietina_ is not an acid but a quinone and
is better termed physcion.

_Colour Reactions of Lichens._--The classification of lichens is
unique in the fact that chemical colour reactions are used by many
lichenologists in the discrimination of species, and these reactions
are included in the specific diagnoses. The substances used as tests
in these reactions are caustic potash and calcium hypochlorite; the
former being the substance dissolved in an equal weight of water and
the latter a saturated extract of bleaching powder in water. These
substances are represented by lichenologists by the signs K and CaCl
respectively, and the presence or absence of the colour reactions are
represented thus, K+, CaCl+, or K-, CaCl-. If the cortical layer
should exhibit positive reaction and the medulla of the same species a
negative reaction with both reagents, the result is represented thus,
K±CaCl±. If a reaction is only produced after the consecutive addition
of the two reagents, this is symbolized by K(CaCl)+. A solution of
iodine is also used as a test owing to the blue or wine-red colour
which the thallus, hymenium or spores may give with this reagent. The
objection to the case of these colour reactions is due to the
indefinite nature of the reaction and the doubt as to the constant
presence of a definite chemical compound in a given species. A yellow
colour with caustic potash solution is produced not only by atranoric
acid but also by evernic acid, thamnolic acid, &c. Again in the case
of _Xanthoria parietina_ vulpinic acid is only to be found in young
thalli growing on sandstone; in older forms or in those growing on
another substratum it is not to be detected. A similar relation
between oil formation and the nature of the substratum has been
observed in many lichens. Considerations such as these should make one
very wary in placing reliance on these colour reactions for the
purposes of classification.

_Economic Uses of Lichens._

In the arts, as food and as medicine, many lichens have been highly esteemed, though others are not now employed for the same purposes as formerly.

1. _Lichens Used in the Arts._--Of these the most important are such as yield, by maceration in ammonia, the dyes known in commerce as archil, cudbear and litmus. These, however, may with propriety be regarded as but different names for the same pigmentary substance, the variations in the character of which are attributable to the different modes in which the pigments are manufactured. Archil proper is derived from several species of _Roccella_ (e.g. _R. Montaguei_, _R. tinctoria_), which yield a rich purple dye; it once fetched a high price in the market. Of considerable value is the "perelle" prepared from _Lecanora parella_, and used in the preparation of a red or crimson dye. Inferior to this is "cudbear," derived from _Lecanora tartarea_, which was formerly very extensively employed by the peasantry of north Europe for giving a scarlet or purple colour to woollen cloths. By adding certain alkalies to the other ingredients used in the preparation of these pigments, the colour becomes indigo-blue, in which case it is the litmus of the Dutch manufacturers. Amongst other lichens affording red, purple or brown dyes may be mentioned _Ramalina scopulorum_, _Parmelia_, _saxatilis_ and _P. amphalodes_, _Umbilicaria pustulata_ and several species of _Gyrophora_, _Urceolaria scruposa_, all of which are more or less employed as domestic dyes. Yellow dyes, again, are derived from _Chlorea vulpina_, _Platysma juniperinum_, _Parmelia caperata_ and _P. conspersa_, _Physcia flavicans_, _Ph. parietina_ and _Ph. lychnea_, though like the preceding they do not form articles of commerce, being merely used locally by the natives of the regions in which they occur most plentifully. In addition to these, many exotic lichens, belonging especially to _Parmelia_ and _Sticta_ (e.g. _Parmelia tinctorum_, _Sticta argyracea_), are rich in colouring matter, and, if obtained in sufficient quantity, would yield a dye in every way equal to archil. These pigments primarily depend upon special acids contained in the thalli of lichens, and their presence may readily be detected by means of the reagents already noticed. In the process of manufacture, however, they undergo various changes, of which the chemistry is still but little understood. At one time also some species were used in the arts for supplying a gum as a substitute for gum-arabic. These were chiefly _Ramalina fraxinea_, _Evernia prunastri_ and _Parmelia physodes_, all of which contain a considerable proportion of gummy matter (of a much inferior quality, however, to gum-arabic), and were employed in the process of calico-printing and in the making of parchment and cardboard. In the 17th century some filamentose and fruticulose lichens, viz. species of _Usnea_ and _Ramalina_, also _Evernia furfuracea_ and _Cladonia rangiferina_, were used in the art of perfumery. From their supposed aptitude to imbibe and retain odours, their powder was the basis of various perfumes, such as the celebrated "Poudre de Cypre" of the hairdressers, but their employment in this respect has long since been abandoned.

2. _Nutritive Lichens._--Of still greater importance is the capacity of many species for supplying food for man and beast. This results from their containing starchy substances, and in some cases a small quantity of saccharine matter of the nature of mannite. One of the most useful nutritious species is _Cetraria islandica_, "Iceland moss," which, after being deprived of its bitterness by boiling in water, is reduced to a powder and made into cakes, or is boiled and eaten with milk by the poor Icelander, whose sole food it often constitutes. Similarly _Cladonia rangiferina_ and _Cl. sylvatica_, the familiar "reindeer moss," are frequently eaten by man in times of scarcity, after being powdered and mixed with flour. Their chief importance, however, is that in Lapland and other northern countries they supply the winter food of the reindeer and other animals, who scrape away the snow and eagerly feed upon them. Another nutritious lichen is the "Tripe de Roche" of the arctic regions, consisting of several species of the _Gyrophorei_, which when boiled is often eaten by the Canadian hunters and Red Indians when pressed by hunger. But the most singular esculent lichen of all is the "manna lichen," which in times of drought and famine has served as food for large numbers of men and cattle in the arid steppes of various countries stretching from Algiers to Tartary. This is derived chiefly from _Lecanora esculenta_, which grows unattached on the ground in layers from 3 to 6 in. thick over large tracts of country in the form of small irregular lumps of a greyish or white colour. In connexion with their use as food we may observe that of recent years in Scandinavia and Russia an alcoholic spirit has been distilled from _Cladonia rangiferina_ and extensively consumed, especially in seasons when potatoes were scarce and dear. Formerly also _Sticta pulmonaria_ was much employed in brewing instead of hops, and it is said that a Siberian monastery was much celebrated for its beer which was flavoured with the bitter principle of this species.

3. _Medicinal Lichens._--During the middle ages, and even in some quarters to a much later period, lichens were extensively used in medicine in various European countries. Many species had a great repute as demulcents, febrifuges, astringents, tonics, purgatives and anthelmintics. The chief of those employed for one or other, and in some cases for several, of these purposes were _Cladonia pyxidata_, _Usnea barbata_, _Ramalina farinacea_, _Evernia prunastri_, _Cetraria ìslandica_, _Sticla pulmonaria_, _Parmelia saxatilis_, _Xanthoria parietina_ and _Pertusaria amara_. Others again were believed to be endowed with specific virtues, e.g. _Peltigera canina_, which formed the basis of the celebrated "pulvis antilyssus" of Dr Mead, long regarded as a sovereign cure for hydrophobia; _Platysma juniperinum_, lauded as a specific in jaundice, no doubt on the _similia similibus_ principle from a resemblance between its yellow colour and that of the jaundiced skin; _Peltidea aphthosa_, which on the same principle was regarded by the Swedes, when boiled in milk, as an effectual remedy for the _aphthae_ or rash on their children. Almost all of these virtues, general or specific, were imaginary; and at the present day, except perhaps in some remoter districts of northern Europe, only one of them is employed as a remedial agent. This is the "Iceland moss" of the druggists' shops, which is undoubtedly an excellent demulcent in various dyspeptic and chest complaints. No lichen is known to be possessed of any poisonous properties to man, although _Chlorea vulpina_ is believed by the Swedes to be so. Zukal has considered that the lichen acids protect the lichen from the attacks of animals; the experiments of Zopf, however, have cast doubt on this; certainly lichens containing very bitter acids are eaten by mites though some of the acids appear to be poisonous to frogs.

_Classification._

The dual nature of the lichen thallus introduces at the outset a classificatory difficulty. Theoretically the lichens may be classified on the basis of their algal constituent, on the basis of their fungal constituent, or they may be classified as if they were homogeneous organisms. The first of these systems is impracticable owing to the absence of algal reproductive organs and the similarity of the algal cells (gonidia) in a large number of different forms. The second system is the most obvious one, since the fungus is the dominant partner and produces reproductive organs. The third system was that of Nylander and his followers, who did not accept the Schwenderian doctrine of duality. In actual practice the difference between the second and third methods is not very great since the fungus is the producer of the reproductive organs and generally the main constituent. Most systems agree in deriving the major divisions from the characters of the reproductive organs (perithecia, apothecia, or basidiospore bearing fructification), while the characters of the algal cells and those of the thallus generally are used for the minor divisions. The difference between the various systems lies in the relative importance given to the reproductive characters on the one hand and the vegetative characters on the other. In the system (1854-1855) of Nylander the greater weight is given to the latter, while in more modern systems the former characters receive the more attention.

A brief outline of a system of classification, mainly that of Zahlbruckner as given in Engler and Prantl's _Pflanzenfamilien_, is outlined below.

There are two main divisions of lichens, _Ascolichenes_ and _Basidiolichenes_, according to the nature of the fungal element, whether an ascomycete or basidiomycete. The Ascolichenes are again divided into _Pyrenocarpeae_ or _Pyrenolichenes_ and _Gymnocarpeae_ or _Discolichenes_; the first having an ascocarp of the nature of a perithecium, the second bearing their ascospores in an open apothecium.

PYRENOLICHENES

Series I. Perithecium simple not divided.

a. With _Pleurococcus_ or _Palmella_ gonidia. Moriolaceae,
Verrucariaceae, Pyrenothamnaceae.

b. With _Chroolepus_ gonidia. Pyrenulaceae, Paratheliaceae.

c. With _Phyllactidium_ or _Cephaleurus_ gonidia. Strigulaceae.

d. With _Nostoc_ or _Scytonema_ gonidia. Pyrenidiaceae.

Series II. Perithecia divided or imperfectly divided by cross-walls. Mycoporaceae with _Palmella_ or _Chroolepus_ gonidia.

DISCOLICHENES

Series I. Coniocarpineae. The paraphyses branch and form a network (capillitium) over the asci, the capillitium and ejected spores forming a long persistent powdery mass (mazaedium).

Caliciaceae, Cypheliaceae, Sphaerophoraceae.

Series II. Graphidineae. Apothecia seldom round, usually elongated-ellipsoidal, no capillitium. Arthoniaceae, Graphidiaceae, Roccellaceae.

Series III. Cyclocarpineae, Apothecium usually circular, no capillitium.

A. Spores usually two-celled, either with a strongly thickened
cross-wall often perforated by a narrow canal or with cross-wall only
slightly thickened. In the first case the spores are usually
colourless, the second case always brown. Buelliaceae, Physciaceae.

B. Spores unicellular, parallel-multicellular or muriform, usually
colourless, cross-walls usually thin.

[alpha] Thallus in moist state more or less gelatinous. Gonidia
always belonging to the Cyanophyceae, Lichinaceae, Ephebaceae,
Collemaceae, Pyrenopsidaceae.

ß Thallus not gelatinous. Coenogoniaceae, Lecideaceae, Cladoniaceae,
Lecanoraceae, Pertusariaceae, Peltigeraceae, Stictaceae,
Pannariaceae, Gyrophoraceae, Parmeliaceae, Cladoniaceae, Usneaceae.

BASIDIOLICHENES (Hymenolichenes)

_Cora_, _Dictyonema_ (incl. Laudatea), _Corella_ (doubtfully placed here as the hymenium is unknown).

_Habitats and Distribution of Lichens._

1. _Habitats._--These are extremely varied, and comprise a great number of very different substrata. Chiefly, however, they are the bark of trees, rocks, the ground, mosses and, rarely, perennial leaves. (a) With respect to _corticolous_ lichens, some prefer the rugged bark of old trees (e.g. _Ramalina_, _Parmelia_, _Stictei_) and others the smooth bark of young trees and shrubs (e.g. _Graphidei_ and some _Lecideae_). Many are found principally in large forests (e.g. _Usnea_, _Alectoria jubata_); while a few occur more especially on trees by roadsides (e.g. _Physcia parietina_ and _Ph. pulverulenta_). In connexion with corticolous lichens may be mentioned those _lignicole_ species which grow on decayed, or decaying wood of trees and on old pales (e.g. _Caliciei_, various _Lecideae_, _Xylographa_), (b) As to _saxicolous_ lichens, which occur on rocks and stones, they may be divided into two sections, viz. _calcicolous_ and _calcifugous_. To the former belong such as are found on calcareous and cretaceous rocks, and the mortar of walls (e.g. _Lecanora calcarea_, _Lecidea calcivora_ and several _Verrucariae_), while all other saxicolous lichens may be regarded as belonging to the latter, whatever may be the mineralogical character of the substratum. It is here worthy of notice that the apothecia of several calcicolous lichens (e.g. _Lecanora Prevostii_, _Lecidea calcivora_) have the power of forming minute cavities in the rock, in which they are partially buried. (c) With respect to terrestrial species, some prefer peaty soil (e.g. _Cladonia_, _Lecidea decolorans_), others calcareous soil (e.g. _Lecanora crassa_, _Lecidea decipiens_), others sandy soil or hardened mud (e.g. _Collema limosum_, _Peltidea venosa_); while many may be found growing on all kinds of soil, from the sands of the sea-shore to the granitic detritus of lofty mountains, with the exception of course of cultivated ground, there being no agrarian lichens. (d) _Muscicolous_ lichens again are such as are most frequently met with on decayed mosses and _Jungermannia_, whether on the ground, trees or rocks (e.g. _Leptogium muscicola_, _Gomphillus calicioides_). (e) The _epiphyllous_ species are very peculiar as occurring upon perennial leaves of certain trees and shrubs, whose vitality is not at all affected by their presence as it is by that of fungi. In so far, however, as is known, they are very limited in number (e.g. _Lecidea_, _Bouteillei_, _Strigula_).

Sometimes various lichens occur abnormally in such unexpected habitats as dried dung of sheep, bleached bones of reindeer and whales, old leather, iron and glass, in districts where the species are abundant. It is apparent that in many cases lichens are quite indifferent to the substrata on which they occur, whence we infer that the preference of several for certain substrata depends upon the temperature of the locality or that of the special habitat. Thus in the case of saxicolous lichens the mineralogical character of the rock has of itself little or no influence upon lichen growth, which is influenced more especially and directly by their physical properties, such as their capacity for retaining heat and moisture. As a rule lichens grow commonly in open exposed habitats, though some are found only or chiefly in shady situations; while, as already observed, scarcely any occur where the atmosphere is impregnated with smoke. Many species also prefer growing in moist places by streams, lakes and the sea, though very few are normally and probably none entirely, _aquatic_, being always at certain seasons exposed for a longer or shorter period to the atmosphere (e.g. _Lichina_, _Leptogium rivulare_, _Endocarpon fluviatile_, _Verrucaria maura_). Some species are entirely parasitical on other lichens (e.g. various _Lecideae_ and _Pyrenocarpei_), and may be peculiar to one (e.g. _Lecidea vitellinaria_) or common to several species (e.g. _Habrothallus parmeliarum_). A few, generally known as _erratic_ species, have been met with growing unattached to any substratum (e.g. _Parmella revoluta_, var. _concentrica_, _Lecanora esculenta_); but it can hardly be that these are really free _ab initio_ (_vide_ Crombie in _Journ. Bot._, 1872, p. 306). It is to the different characters of the stations they occupy with respect to exposure, moisture, &c., that the variability observed in many types of lichens is to be attributed.

2. _Distribution._--From what has now been said it will readily be inferred that the distribution of lichens over the surface of the globe is regulated, not only by the presence of suitable substrata, but more especially by climatic conditions. At the same time it may safely be affirmed that their geographical range is more extended than that of any other class of plants, occurring as they do in the coldest and warmest regions--on the dreary shores of arctic and antarctic seas and in the torrid valleys of tropical climes, as well as on the greatest mountain elevations yet attained by man, on projecting rocks even far above the snowline (e.g. _Lecidea geographica_). In arctic regions lichens form by far the largest portion of the vegetation, occurring everywhere on the ground and on rocks, and fruiting freely; while terrestrial species of _Cladonia_ and _Stereocaulon_ are seen in the greatest luxuriance and abundance spreading over extensive tracts almost to the entire exclusion of other vegetation. The lichen flora of temperate regions again is essentially distinguished from the preceding by the frequency of corticolous species belonging to _Lecanora_, _Lecidea_ and _Graphidei_. In intertropical regions lichens attain their maximum development (and beauty) in the foliaceous _Stictei_ and _Parmeliei_, while they are especially characterized by epiphyllous species, as _Strigula_, and by many peculiar corticole _Thelotremei_, _Graphidei_ and _Pyrenocarpei_. Some lichens, especially saxicolous ones, seem to be cosmopolitan (e.g. _Lecanora subfusca_, _Cladonia pyxidata_); and others, not strictly cosmopolitan, have been observed in regions widely apart. A considerable number of species, European and exotic, seem to be _endemic_, but further research will no doubt show that most of them occur in other climatic regions similar to those in which they have hitherto alone been detected. To give any detailed account, however, of the distribution of the different genera (not to speak of that of individual species) of lichens would necessarily far exceed available limits.

BIBLIOGRAPHY.--General: Engler and Prantl, _Die natürlichen
Pflanzenfamilien_, Teil I, Abt. 1 * where full literature will be
found up to 1898. M. Funfstuck, "Der gegenwärtige Stand der
Flechtenkunde," _Refer. Generalvers. d. deut. bot. Ges._ (1902). Dual
Nature: J. Baranetzky, "Beiträge zur Kenntnis des selbstständigen
Lebens der Flechtengonidien," _Prings. Jahrb. f. wiss. Bot._ vii.
(1869); E. Bornet, "Recherches sur les gonidies des lichens," _Ann. de
sci. nat. bot._, 5 sér. n. 17 (1873); G. Bonnier, "Recherches sur la
synthèse des lichens," _Ann. de sci. nat. bot._, 7 sér. n. 9 (1889);
A. Famintzin and J. Baranetzky, "Zur Entwicklungsgeschichte der
Gonidien u. Zoosporenbildung der Lichenen," _Bot. Zeit._ (1867, p.
189, 1868, p. 169); S. Schwendener, _Die Algentypen der
Flechtengonidien_ (Basel, 1869); A. Möller, _Über die Kultur
flechtenbildender Ascomyceten ohne Algen_. (Münster, 1887). Sexuality:
E. Stahl, _Beiträge zur Entwickelungsgeschichte der Flechten_
(Leipzig, 1877); G. Lindau, _Über Anlage und Entwickelung einiger
Flechtenapothecien_ (Flora, 1888); E. Baur, "Zur Frage nach der
Sexualität der Collemaceae," _Ber. d. deut. bot. Ges._ (1898); "Über
Anlage und Entwicklung einiger Flechtenapothecien" (_Flora_, Bd. 88,
1901); "Untersuchungen über die Entwicklungsgeschichte der
Flechtenapothecien," _Bot. Zeit._ (1904); O. V. Darbishire, "Über die
Apothecium-entwickelung der Flechte, Physcia pulverulenta," _Nyl.
Prings. Jahrb._ (Bd. 34, 1900). Chemistry.--W. Zopf, "Vergleichende
Produkte," _Beitr. z. bot. Centralbl._ (Bd. 14, 1903); _Die
Flechtenstoffe_ (Jena, 1907). (J. M. C; V. H. B.)

FOOTNOTE:

[1] The _thalline margin_ (margo thallinus) is the projecting edge of
a special layer of thallus, the amphithecium, round the actual
apothecium; the _proper margin_ (margo proprius) is the projecting
edge of the apothecium itself.

LICHFIELD, a city, county of a city, and municipal borough in the Lichfield parliamentary division of Staffordshire, England, 118 m. N.W. from London. Pop. (1901) 7902. The London and North-Western railway has stations at Trent Valley Junction on the main line, and in the city on a branch westward. The town lies in a pleasant country, on a small stream draining eastward to the Trent, with low hills to the E. and S. The cathedral is small (the full internal length is only 370 ft., and the breadth of the nave 68 ft.), but beautiful in both situation and style. It stands near a picturesque sheet of water named Minster Pool. The present building dates from various periods in the 13th and early 14th centuries, but the various portions cannot be allocated to fixed years, as the old archives were destroyed during the Civil Wars of the 17th century. The earlier records of the church are equally doubtful. A Saxon church founded by St Chad, who was subsequently enshrined here, occupied the site from the close of the 7th century; of its Norman successor portions of the foundations have been excavated, but no record exists either of its date or of its builders. The fine exterior of the cathedral exhibits the feature, unique in England, of a lofty central and two lesser western spires, of which the central, 252 ft. high, is a restoration attributed to Sir Christopher Wren after its destruction during the Civil Wars. The west front is composed of three stages of ornate arcading, with niches containing statues, of which most are modern. Within, the south transept shows simple Early English work, the north transept and chapter house more ornate work of a later period in that style, the nave, with its geometrical ornament, marks the transition to the Decorated style, while the Lady chapel is a beautiful specimen of fully developed Decorated work with an apsidal east end. The west front probably falls in date between the nave and the Lady chapel. Among numerous monuments are--memorials to Samuel Johnson, a native of Lichfield, and to David Garrick, who spent his early life and was educated here; a monument to Major Hodson, who fell in the Indian mutiny, and whose father was canon of Lichfield; the tomb of Bishop Hacket, who restored the cathedral after the Civil Wars; and a remarkable effigy of Perpendicular date displaying Sir John Stanley stripped to the waist and awaiting chastisement. Here is also the "Sleeping Children," a masterpiece by Chantrey (1817).

A picturesque bishop's palace (1687) and a theological college (1857) are adjacent to the cathedral. The diocese covers the greater part of Staffordshire and about half the parishes in Shropshire, with small portions of Cheshire and Derbyshire. The church of St Chad is ancient though extensively restored; on its site St Chad is said to have occupied a hermit's cell. The principal schools are those of King Edward and St Chad. There are many picturesque half-timbered and other old houses, among which is that in which Johnson was born, which stands in the market-place, and is the property of the corporation and opened to the public. There is also in the market place a statue to Johnson. A fair is held annually on Whit-Monday, accompanied by a pageant of ancient origin. Brewing is the principal industry, and in the neighbourhood are large market gardens. The city is governed by a mayor, 6 aldermen and 18 councillors. Area, 3475 acres.

There is a tradition that "Christianfield" near Lichfield was the site of the martyrdom of a thousand Christians during the persecutions of Maximian about 286, but there is no evidence in support of the tradition. At Wall, 3 m. from the present city, there was a Romano-British village called Letocetum ("grey wood"), from which the first half of the name Lichfield is derived. The first authentic notice of Lichfield (_Lyecidfelth_, _Lychfeld_, _Litchfield_) occurs in Bede's history where it is mentioned as the place where St Chad fixed the episcopal see of the Mercians. After the foundation of the see by St Chad in 669, it was raised in 786 by Pope Adrian through the influence of Offa, King of Mercia, to the dignity of an archbishopric, but in 803 the primacy was restored to Canterbury. In 1075 the see of Lichfield was removed to Chester, and thence a few years later to Coventry, but it was restored in 1148. At the time of the Domesday Survey Lichfield was held by the bishop of Chester: it is not called a borough, and it was a small village, whence, on account of its insignificance, the see had been moved. The lordship and manor of the town were held by the bishop until the reign of Edward VI., when they were leased to the corporation. There is evidence that a castle existed here in the time of Bishop Roger Clinton (_temp._ Henry I.), and a footpath near the grammar-school retains the name of Castle-ditch. Richard II. gave a charter (1387) for the foundation of the gild of St Mary and St John the Baptist; this gild obtained the whole local government, which it exercised until its dissolution by Edward VI., who incorporated the town (1548), vesting the government in two bailiffs and twenty-four burgesses; further charters were given by Mary, James I. and Charles II. (1664), the last, incorporating it under the title of the "bailiffs and citizens of the city of Lichfield," was the governing charter until 1835; under this charter the governing body consisted of two bailiffs and twenty-four brethren. Lichfield sent two members to the parliament of 1304 and to a few succeeding parliaments, but the representation did not become regular until 1552; in 1867 it lost one member, and in 1885 its representation was merged in that of the county. By the charter of James I. the market day was changed from Wednesday to Tuesday and Friday; the Tuesday market disappeared during the 19th century; the only existing fair is a small pleasure fair of ancient origin held on Ash-Wednesday; the annual fête on Whit-Monday claims to date from the time of Alfred. In the Civil Wars Lichfield was divided. The cathedral authorities with a certain following were for the king, but the townsfolk generally sided with the parliament, and this led to the fortification of the close in 1643. Lord Brooke, notorious for his hostility to the church, came against it, but was killed by a deflected bullet on St Chad's day, an accident welcomed as a miracle by the Royalists. The close yielded and was retaken by Prince Rupert in this year; but on the breakdown of the king's cause in 1646 it again surrendered. The cathedral suffered terrible damage in these years.

See Rev. T. Harwood, _Hist. and Antiquities of Church and City of
Lichfield_ (1806), _Victoria County History, Stafford_.

LICH-GATE, or LYCH-GATE (from O. Eng. _lic_ "a body, a corpse"; cf. Ger. _Leiche_), the roofed-in gateway or porch-entrance to churchyards. Lich-gates existed in England certainly thirteen centuries ago, but comparatively few early ones survive, as they were almost always of wood. One at Bray, Berkshire, is dated 1448. Here the clergy meet the corpse and some portion of the service is read. The gateway was really part of the church; it also served to shelter the pall-bearers while the bier was brought from the church. In some lich-gates there stood large flat stones called lich-stones upon which the corpse, usually uncoffined, was laid. The most common form of lich-gate is a simple shed composed of a roof with two gabled ends, covered with tiles or thatch. At Berrynarbor, Devon, there is a lich-gate in the form of a cross, while at Troutbeck, Westmorland, there are three lich-gates to one churchyard. Some elaborate gates have chambers over them. The word _lich_ entered into composition constantly in old English, thus, lich-bell, the hand-bell rung before a corpse; lich-way, the path along which a corpse was carried to burial (this in some districts was supposed to establish a right-of-way); lich-owl, the screech-owl, because its cry was a portent of death; and lyke-wake, a night watch over a corpse.