To this series belong the lowest of the Basidiomycetes. The _basidia_
appear in two principal forms (1 and 2 on page 144) and are _divided_
into four cells, either transversely or longitudinally, each division
forming a sterigma which abstricts a basidiospore. The first three
orders, Uredinaceæ, Auriculariaceæ, and Tremellaceæ have _gymnocarpic_
fruit-bodies, while those of the Pilacraceæ, on the contrary, are
_angiocarpic_.
Order 1. =Uredinaceæ (Rusts).= All the Rust-Fungi are parasites, their
mycelium living in the interior of the stems and leaves of their
hosts, causing red, brown, or black spots--hence their name--and
malformations, sometimes of considerable size.
The Rust-Fungi are gymnocarpic and destitute of a hymenium; for these
reasons they are regarded as the simplest order of the Basidiomycetes.
They are entirely parasitic, and their filamentous, branched mycelium
ramifies in the intercellular spaces of its host, and often protrudes
haustoria into the cells. The mycelium is perennial should it enter a
woody tissue; it may also hibernate in the rhizomes of perennial herbs
and permeate the shoots springing from them, but in the majority of
the Rust-Fungi the mycelium has a very limited growth. The chief means
of reproduction of the Rust-Fungi are the _chlamydospores_, which in
the more highly developed species occur in three forms, namely, the
teleuto-, æcidio-, and uredo-spores. The spores, in the host, are
formed immediately beneath its epidermis, which is ruptured on the
ripening of the spores, with the production of “rust,” brown, red, or
black spots. Those chlamydospores which produce basidia are termed
_teleutospores_. The spore on germination produces a _transversely
divided basidium_, “promycelium,” on which basidiospores, “sporidia,”
generally four in number, are produced on lateral sterigmata. This
basidio-fructification is _gymnocarpic_; the basidia neither form a
hymenium nor a fruit-body (only _Cronartium_ and _Gymnosporangium_ have
a slight indication of a basidio-fructification).
Many Rust-Fungi, in addition to basidiospores, have small, _unicellular
conidia_, “spermatia,” which are borne in conidiocarps, “_spermogonia_.”
The ~TELEUTOSPORES~ (_Winter-spores_) may be either unicellular or
multicellular; in the majority of cases they are enclosed in a hard
outer cell-wall, the exospore, which in some cases is very strongly
developed; they have also a long or short stalk, the remains of the
spore-bearing hypha. Each cell of the teleutospore has _one germ-pore_
(a thin portion of the wall, for the protrusion of the germ-tube;
in _Phragmidium_ and _Gymnosporangium_ there are, however, several
germ-pores). The colour of the teleutospores is generally much darker
than that of the uredospores, and it is by these that the majority of
the Rust-Fungi _hibernate_.
In _Gymnosporangium_, two kinds of teleutospores are found
(distinguished by their size and thickness of exospore). In many
species of _Puccinia_, the form of the teleutospores varies
very much, so that in the same layer spores have been observed
with the characteristic form of other, allied genera.--The
teleutospores of _Endophyllum_ resemble æcidiospores, since they
are united in chains, whose cells are easily separated, and are
produced in the interior of a “peridium.” The multicellular
teleutospores of _Coleosporium_ function as basidia, and from
each cell immediately produce basidiospores.--The teleutospores
of _Coleosporium_ and _Chrysomyxa_, differ from other
teleutospores in the absence of exospore and germ-pore.
The ÆCIDOSPORES (_Spring-spores_) are produced in chains which are
generally enclosed in an _envelope_ of hyphæ, the _peridium_; the
_peridium_ enclosing the spores being termed the _æcidium_. The
æcidiospores are unicellular, and generally of an orange colour; they
are often separated by intermediate cells which wither and so assist
in the distribution of the spores. The exospore is made up of minute,
radially arranged rods. _Generally germination_ proceeds _immediately_,
the æcidiospore producing a germ-tube, which developes into a mycelium
bearing either uredo- or teleutospores.
The æcidia of many Rust-Fungi were formerly considered as
distinct genera. The æcidia of _Phragmidium_, _Triphragmium_,
and _Melampsora_, in which the _peridium is wanting_, were in
part considered as _Cæoma_. The æcidia with fimbriate edge,
or those of _Gymnosporangium_ with longitudinal lattice-like
splits, were considered as “_Rœstelia_” (Lattice-Rust); large,
sac-shaped æcidia on the Coniferæ were known as _Peridermium_.
The ~UREDOSPORES~ (_Summer-spores_) are unicellular and arise singly,
seldom in chains (_Coleosporium_). Their colourless, warty exospore
bears, _in the equatorial plane_, 2–8 _germ-pores_. In the majority,
_germination_ proceeds _immediately_, and a mycelium is produced which
at first gives rise to uredospores and afterwards to teleutospores.
The uredospore-formations of _Melampsorella_ and _Cronartium_
are enclosed in an _envelope_, and hence resemble
æcidia.--Between the uredospores sterile, unicellular hyphæ
(paraphyses) may be found.
The _spermogonia_ are spherical or pear-shaped _conidiocarps_,
generally embedded in the substratum, and are produced before the
æcidia, before or simultaneously with the uredospores, or before the
teleutospores. The conidia, as far as observations go, do not generally
germinate under ordinary conditions.
Among the Rust-Fungi some species are found which only form
basidiospores and teleutospores (_Puccinia malvacearum_, _Chrysomyxa
abietis_). Other species have in addition uredospores; others
spermogonia and uredospores; others spermogonia and æcidia; others
spermogonia, uredospores and æcidia. Those species in which all the
methods of reproduction are not developed must not be considered as
incomplete forms.
As a rule the mycelium, which is produced from the basidiospores,
developes æcidia; in the species, however, without æcidia, it
developes the uredo-form, and when the uredospores are also absent,
the teleutospore-form. It has been established in some species
of _Puccinia_ and _Uromyces_ that the formation of æcidia can be
suppressed, and it is not a necessary part of the cycle of development
of the species.
The majority of Rust-Fungi hibernate in the teleutospore-form.
Many species are able to hibernate in the uredospore-form
(_Coleosporium senecionis_). Others pass the winter in the
æcidio-form, and develope æcidia on new hosts (_Uromyces pisi_,
on _Euphorbia cyparissias_; _Phragmidium subcorticium_, on
_Rosa_; _Æcidium elatinum_, on _Abies alba_). In _Chrysomyxa
abietis_, the mycelium, developed from the basidiospores,
survives the winter.
Among the Rust-Fungi, with several forms of reproduction, there are
about sixty whose development can only be completed by an _alternation
of hosts_, that is, on one host only uredo-and teleutospores
are produced, while the further development of the germinating
basidiospores, and the formation of the æcidia and spermogonia from its
mycelium, can only take place on a second quite distinct and definite
host (_heterœcious_ or _metoxenous_ Fungi). Those Fungi which have all
their forms of reproduction on the same host are termed _autœcious_ or
_autoxenous_. It is not, however, always necessary that the heterœcious
Rust-Fungi should regularly change their hosts; for example, _Puccinia
graminis_ can hibernate in the uredo-form on the wild Grasses, and in
the spring can distribute itself again in the same form.
As a consequence of the alternation of hosts the various forms
of development were considered as independent genera (_Uredo_,
_Æcidium_, _Rœstelia_, _Cæoma_, _Peridermium_), until De Bary
and Oersted established, about the same time (1865), the mutual
connection of some forms, and paved the way for the right
conception of these Fungi.
[Illustration: FIG. 146.--_Puccinia graminis_.]
As an example of one of the most highly developed species, _Puccinia
graminis_, the “Rust of Wheat,” holds a prominent position. Its
uredospores and teleutospores are produced (Fig. 146) on Grasses
(on cereals, especially Wheat, Rye, Oats, and many wild Grasses),
while the æcidia and spermogonia are confined to the Berberidaceæ.
The teleutospores, developed on the Grasses, hibernate on the dried
portions of their host, and in the succeeding year each of the
two cells of the teleutospore may develop a _basidium_ with four
basidiospores (Fig. 146 _D_, _c_). The basidiospores are distributed by
the wind, germinate quickly, and only proceed to further development on
_Berberis_ or _Mahonia_. The germ-tube _bores through the epidermis_ of
the Barberry-leaf, and forms a mycelium in its interior, its presence
being indicated by reddish-yellow spots on the leaf. After 6–10 days
the flask-shaped _spermogonia_ appear (Fig. 147 _B_; _C_, _a_; conidia
in Fig. 147 _D_) and a few days later the cup-shaped _æcidia_ (Fig.
147 _A_; _C_, _c_, _d_, _e_). The former are generally on the _upper_,
and the latter on the _under side_ of the leaf. The orange-coloured
æcidiospores scatter like dust, and germinate only on Grasses; the
germination takes place in about two days when placed on any green
part of a Grass. The germ-tube enters the Grass-leaf through a stoma;
a mycelium is developed in the leaf, giving rise to a small, oval,
rust-coloured spot (Fig. 146 _A_); in about 6–9 days the epidermis is
ruptured over the red spot, and numerous reddish-yellow _uredospores_,
formed on the mycelium, are set free. The uredospores (Fig. 146 _B_)
are scattered by the wind, and can germinate should they fall on the
green portions of other Grasses: they then emit 2–4 germ-tubes through
the equatorially-placed germ-pores. The germ-tubes enter a leaf through
a stoma, a new mycelium is then developed, and in about eight days
a fresh production of uredospores takes place, which germinate as
before. The uredospore-mycelium very soon produces, in addition, the
brown _teleutospores_, which give a brown colour to the rust-coloured
spots, the familiar uredospores on the cereals being quite suppressed
towards the close of the summer (Fig. 146 _C, D_). The “Rust of Wheat”
hibernates on some wild Grasses in the uredospore-form.
[Illustration: FIG. 147.--_Æcidium berberidis_. _A_ Portion of
lower surface of leaf of Barberry, with cluster-cups (æcidia).
_B_ A small portion of leaf, with spermogonia, from above. _C_
Transverse section of leaf on the upper side, in the palisade
parenchyma are three spermogonia (_a b_); on the lower side an
unripe æcidium (_c d_) and two ripe æcidia (_d, e, f_); _f_ chain
of æcidiospores. _D_ Hyphæ, forming conidia.]
GENERA. _Puccinia_ (Fig. 146, 147) has bicellular teleutospores,
each having a germ-pore, and the æcidia when present have an
indented peridium; some species, as exceptions, have 1–3-celled
teleutospores. Many species are HETERŒCIOUS, for example, _P.
graminis_, described above; _P. rubigo_, which also infests
various Grasses, but whose æcidia appear on _Anchusa_; the
masses of teleutospores are small; they contain paraphyses, and
are for a long time covered by the epidermis. _P. coronata_, on
Oats and Rye Grass; its æcidia on _Rhamnus_; the teleutospores
are surmounted by a crown--“coronate processes.” _P.
phragmitis_, on Reeds; æcidia on species of _Rumex_ and _Rheum_.
_P. moliniæ_, on _Molinia cœrulea_; the æcidia on Orchids.
_P. poarum_, on Meadow-Grass; æcidia on _Tussilago_. Various
Puccinias growing on species of _Carex_ have their æcidia on
_Urtica_, _Lysimachia_, _Cirsium_, _Pedicularis_, etc.--Of
those AUTŒCIOUS species, which have all their generations on the
same host, may be noted:--_P. galii_, _P. menthæ_, _P. violæ_,
_P. epilobii_, _P. asparagi_, which grow on the hosts from
which they have taken their specific names.--As representative
of a group which have spermogonia, uredo-and teleutospores on
the same host, but on different individuals, _P. suaveolens_,
on the Field-Thistle, may be mentioned. The spermogonia have
a strong odour.--A peculiar group (_Leptopuccinia_) has only
teleutospores, which germinate immediately, and whilst still
attached to their living host. To this group belong _P.
arenariæ_, on a number of Caryophyllaceæ; and _P. malvacearum_,
on various Malvaceæ, introduced in 1873 from South America to
Europe, where it soon proved very destructive to Hollyhocks.
_Uromyces_ (Fig. 149) differs only from _Puccinia_ in always
having unicellular teleutospores. Among this genus both
heterœcious and autœcious species are found. To the first
group belong _U. pisi_, whose æcidia are found on _Euphorbia
cyparissias_, and _U. dactylidis_, whose æcidia appear on
_Ranunculus_; to the second group belong _U. betæ_, _U.
phaseoli_, _U. trifolii_.
_Triphragmium_ has teleutospores with three cells (one below and
two above), on _Spiræa ulmaria_.
_Phragmidium_ (Fig. 150) has teleutospores consisting of a
row of cells (3–10) arranged in a straight line; the upper
cell has one germ-pore and the others four germ-pores placed
equatorially. Both this and the preceding genus have large,
irregular æcidia without peridia, but often with bent, club-like
paraphyses (150 _b_ and _c_); they are all autœcious, and are
only found on the Rosaceæ.
[Illustration: FIG. 148.--_Gymnosporangium sabinæ_. A small
portion of the epidermis of a Pear-leaf (_a_) pierced at _b_ by
the germinating basidiospore (_c_).]
[Illustration: FIG. 149.--_Uromyces genisteæ_; _a_ uredospore;
_b_ teleutospore.]
_Endophyllum_ (see above, under teleutospores, p. 147) on
species of _Sempervivum_.
_Gymnosporangium_ (Figs. 152, 154) has bicellular teleutospores
collected in large, gelatinous masses formed by the swelling of
the long spore-stalks; in each cell 2–4 germ-pores are found.
Uredospores are wanting. All the species are heterœcious; the
teleutospores appear on _Juniperus_, the æcidia (_Rœstelia_)
on the Pomaceæ. _G. sabinæ_, on _Juniperus sabina_, _J.
virginiana_, etc., has the æcidia (“_Rœstelia cancellata_”)
on _Pyrus communis_ (Figs. 152, 148); _G. juniperinum_, on
_Juniperus communis_ with “_Rœstelia cornuta_” (Fig. 154 _a_)
on _Sorbus aucuparia_, _Aria nivea_ (_S. aria_) and _Malus
communis_; _G. clavariæforme_ on _Juniperus communis_, the
æcidium belonging to it (“_Rœstelia lacerata_”) on _Cratægus
oxyacantha_.
_Melampsora_ has prismatic teleutospores placed parallel to each
other and forming a crustaceous layer; in many species they
are divided longitudinally into several cells (Fig. 151). The
æcidia, without peridium, belonged to the old genus _Cæoma_.
_M. caprearum_, on Willows, has the æcidia (_Cæoma euonymi_) on
_Euonymus_. _M. hartigii_, on Osiers; the æcidium on _Ribes_.
_M. mixta_, on _Salix repens_ and Orchids. _M. pinitorqua_,
on leaves of the Aspen, æcidia on Pine branches (Pine shoot
fungus); _M. populina_ on _Populus monilifera_ and _nigra_; _M.
betulina_ (Fig. 153), on Birch leaves; _M. padi_ (Fig. 151),
on leaves of _Prunus padus_, developes teleutospores in the
epidermal cells; _M. lini_ is the cause of injury to the Flax;
_M. agrimoniæ_.
[Illustration: FIG. 150.--_Phragmidium gracile_: _a_ an
uredospore; _b_ and _c_ two paraphyses; _d_ a young teleutospore;
_e_ a teleutospore with a basidium and two basidiospores (_s_);
_f_ two series of æcidiospores (_Ph. rosæ_).]
_Calyptospora gœppertiana_; teleutospores on _Vaccinium vitis
idæa_; spermogonia and æcidia on _Abies alba_ (Firneedle-Rust).
_Coleosporium_ (Fig. 155) forms its uredospores in
reddish-yellow chains; for the teleutospores, see page 147.
_C. senecionis_, on the Groundsel; its æcidium (_Peridermium
wolffii_) on Pine-leaves (Fig. 155 a). Other species on
_Sonchus_, _Petasites_, _Campanula_, _Rhinanthaceæ_.
_Chrysomyxa_ (Fig. 156) has bright red, branched
teleutospore-chains; each spore developes a 4-celled basidium.
_C. ledi_, on _Ledum palustre_; its æcidia on the leaves of the
Fir. _C. abietis_ (Fig. 156), without uredo-and æcidiospores;
teleutospores on the leaves of the Fir. In the first summer,
yellow bands are formed on the leaves, and in the following
spring the red cushions of spores.
[Illustration: FIG. 151.--_Melampsora padi_: _a_ and _b_
uredospores; _c-f_ teleutospores, seen from different sides.]
[Illustration: FIG. 152.--Pear-leaf, seen from the under side,
with “_Rœstelia cancellata_”: in different ages (_a_ youngest,
_d_ oldest).]
[Illustration: FIG. 153.--_Melampsora betulina_: _a_ uredospores;
_b_ three contiguous teleutospores, one of which has developed a
basidium with three basidiospores. (× 400.)]
[Illustration: FIG. 154.--_Gymnosporanginum juniperinum_: _a_
a small leaf with three clusters of æcidia (nat. size); _b_
three conidia; _c_ two æcidiospores on one of which are seen the
germ-pores; _d_ a portion of the wall of an æcidium; _e_, _f_ two
teleutospores.]
[Illustration: FIG. 155.--_Coleosporium senecionis_: _a_
Pine-leaves with æcidia (_Peridermium wolffii_) nat. size; _b_
an æcidiospore; _c_ a germinating æcidiospore; _d_ a chain of
uredospores; _e_ a chain of teleutospores of which the terminal
one has germinated and produced a basidiospore (_s_).]
_Cronartium_ (Figs. 157, 159) has unicellular teleutospores
united in numbers to form erect threads or columns; the
uredospores are enclosed in a “peridium”; _C. ribicola_ (Fig.
157), on leaves of Ribes (especially Black Currants); its
æcidia (_Peridermium strobi_, or _P. klebahni_) on the stems
and branches of _Pinus strobus_ (Fig. 159), on which it causes
great damage; _C. asclepiadeum_, on _Vincetoxicum officinale_;
its æcidia (_Peridermium cornui_) on the stems and branches of
_Pinus silvestris_.
[Illustration: FIG. 156.--_Chrysomyxa abietis_: _a_ leaf of the
Fir, with 5 clusters of basidiospores (× 4); _b_ branched rows of
teleutospores springing from the mycelium (_m_).]
[Illustration: FIG. 157.--_Cronartium ribicola_: _a_ mass
of uredospores (× 50); _b_ an uredospore; _c_ a column of
teleutospores (× 60); _d_ a small portion of the same more highly
magnified, with a basidium and two basidiospores (_s_).]
To the Fungi of which the æcidium is known, whilst the remaining
forms are still undetermined, but which are without doubt
heterœcious, belong _Æcidium elatinum_, which produces the
enormous “witches’ brooms” and barrel-shaped swellings on stems
and branches of _Abies alba_; and _Æcidium strobilinum_ (Fig.
158), which attacks Fir-cones, causing all the scales to become
covered with clusters of æcidia opening by a lid. _Hemileia
vastatrix_ destroyed the coffee plantations in Asia.
[Illustration: FIG. 158.--_Æcidium strobilinum_: _a_ scale of
cone of _Picea excelsa_, with numerous æcidia; _b_ æcidiospores
arranged in a series; _c_ a cell of the peridium.]
Order 2. =Auriculariaceæ.= The _long, transversely divided_ basidia
bear laterally 4 _long sterigmata_ with basidiospores (Fig. 160 _B_)
and are united to form an _hymenium_ on the surface of the fruit-body.
Parasites or saprophytes.
_Auricularia sambucina_ (_Auricula judæ_), Judas’-ear, has large
fruit-bodies, which may attain the size of several inches,
resembling an ear or a mussel shell. In the moist condition they
are flesh-coloured, tough and gelatinous, but when dried, become
hard, grey and wrinkled; the exterior is covered with short
hairs; while the internal surface bears the hymenium. Habitat:
stems and branches of old Elder-trees (_Sambucus_).
Order 3. =Tremellaceæ.= The _round, pear-shaped, longitudinally divided
basidia_ bear 4 _elongated sterigmata_, situated apically, and 4
basidiospores (Fig. 160 _C_, _D_), and are united into the _hymenium_
on the surface of the fruit-body. The fruit-bodies are frequently
gelatinous and quivering; similar fruit-bodies are also found in the
Dacryomycetaceæ and Hydnaceæ. Simple conidiophores, which appear not
infrequently in the basidiocarps, before the basidia, are known in many
species. Saprophytes.
[Illustration: FIG. 159.--_Peridermium strobi_: æcidia of
_Cronartium ribicola_ (nat. size).]
[Illustration: FIG. 160.--_B Auricularia sambucina_: _a-d_
basidia in various stages of development; _e_ a sterigma
bearing a spore.--_C Tremella lutescens_: _a-d_ basidia seen
from various sides (_b_ from above) and in various stages of
development; _e_ sterigma with basidiospore (× 400). _D Exidia
glandulosa_: _a-c_ various stages in the development of a
basidium; _d_ sterigma with basidiospore (× 350).]
_Exidia_ has kidney-shaped, oblong basidiospores, and small,
hook-like conidia; _E. glandulosa_, _E. albida_, etc., on
wood.--_Craterocolla_ has conidiocarps; _C. cerasi_ on
Cherry-wood.--_Sebacina incrustans_; the yellow, fleshy, or
cartilaginous fruit-bodies are found in autumn covering the
ground in moist woods.--_Tremella_ has round basidiospores;
_T. mesenterica_ has irregularly-folded, quivering, orange
fruit-bodies, about one inch in breadth; _T. lutescens_ (Fig.
161) has orange-yellow conidial-and yellow basidial-layers; _T.
frondosa_ has fruit-bodies upwards of a foot in breadth.
Order 4. =Pilacraceæ.= The _transversely divided basidia_ have _no
sterigmata_, but sessile basidiospores, and fill up the cavity of a
_closed_ (_angiocarpic_) _fruit-body_ as a gleba without a regular
arrangement (hymenium wanting).
_Pilacre fagi_ on the old stems of the Copper-Beech; _P.
petersii_, on dried branches of the Hornbeam, has stalked,
capitate fruit-bodies.
[Illustration: FIG. 161.--_Tremella lutescens_: I and II
fruit-bodies (nat. size); III vertical section through a
fruit-body; _b_ basidia; _c_ conidia; IV-VI basidia; VII
basidiospore with a second spore; VIII a basidiospore with
yeast-like budding (cultivated); IX a conidiophore. (III-IX about
400.)]