_RUSTS._
A QUARTER of a century ago, and all the fungi enumerated in the
preceding and in the present and following chapters would have been
arranged under three genera, called respectively _Æcidium_, _Puccinia_,
and _Uredo_. Under the last-named genus all the species illustrated in
the present chapter, beside many others, would have found “a habitation
and a name.” There are still a few which bear the old generic name, and,
if only out of respect, we shall grant them the first place.
Let the first bright day in May witness the student beside a cluster of
plants of _Mercurialis perennis_, which it will not be difficult to find
in many localities, and, on turning up the lower leaves, he will meet
with our first illustration of a genuine _Uredo_, in the form of yellow
confluent patches, with a powdery surface (Plate VII. fig. 133). This
will be _Uredo confluens_. By the way, the generic name is in itself
suggestive, which it always should be in all instances, but
unfortunately is not; it is derived from the Latin word _uro_, “I burn,”
and is peculiarly applicable in instances where the leaves acquire a
blistered, burnt, or scorched appearance, occasioned by the presence of
the fungus. The microscopical features of the spores of this genus are,
briefly, a more or less spherical form, without any pedicel or footstalk
Plate VII. fig. 134). These spores are at first produced each in a
separate cell, but when ripe become free, and are at times with
difficulty distinguished from such forms as _Trichobasis_, unless the
pedicels in the early stage of the latter genus are regarded.
A rare species in Britain is the oak-leaf rust (_Uredo Quercus_), in
which the sori or pustules are minute, and at first yellow, but
afterwards orange. It occurs on the under surface of the leaves, and
was, we believe, first found in this country by Mr. D. Stock, in the
neighbourhood of Bungay, nearly five-and-twenty years since. That
gentleman informs us that it was not at all uncommon, but always
appeared on the young shoots which had sprung up from the trunks or
roots of trees that had been cut down. We are uncertain whether it has
been found by any one since that time in this country, although it is
not uncommon in France.
The leaves of the common sorrel are often sparely sprinkled with the
pustules of a rust (_Uredo bifrons_, Grev.), which derives its specific
name from the fact that the pustules, which appear on both surfaces of
the leaves, are often opposite to each other Plate VII. fig. 137). These
pustules are generally seated on a discoloured spot (Plate VII. fig. 138
enlarged), and are surrounded by the remains of the ruptured epidermis.
The spores are globose and brown Plate VII. fig. 139). We have not met
with any other _Uredine_ on the sorrel leaves, though one having a
similar appearance to the naked eye is not uncommon on several species
of dock.
The fern rust (_Uredo Filicum_), which occurs on the under surface of
the fronds of two or three species of ferns, we have never met with, and
do not think that it can be considered common. It has been found in the
West of England, on _Cystopteris_, and Sowerby collected it, probably
not very far from London.
One of the most common is the rust found on the leaves of the
enchanter’s nightshade (_Circæa lutetiana_), sometimes nearly covering
the under surface with its tawny snuff-coloured spores Plate VII. fig.
135). The plant on which it is found is rather local, but the rust
(_Uredo Circææ_) seems to abound wherever the plant on which it is
parasitic flourishes. Another fungus of a very similar external
appearance may be collected, more rarely, from the leaves of the same
plant; but in this the spores are two-celled, or divided by a transverse
partition. This fact is mentioned to guard against disappointment,
should the spores be found to differ from the characters of this
section, and to show that the microscope is essential to the study of
fungi. The spores of the true Uredo are globose and without any
partition Plate VII. fig. 136).
[Illustration:
Plate IX.
W. West imp.
]
We may also observe that a very interesting species may be found on
several species of St. John’s-wort (_Hypericum_), but especially on the
under surface of the leaves of the Tutsan, covering them with its
golden-coloured spores (Plate VIII. fig. 174). Another occurs on the
leaves of some of the wild garlics (_Allium_); one is not uncommon on
some of the stitchworts; another on saxifrages; another on willow-herbs
(_Epilobium_), and one on the leaves of the cowberry. All of these have
yellowish spores. A species with brown spores occurs on sea-lavender
(_Statice_). Space to write on our own part, and patience to read on the
part of others, induce us to dismiss all these species with the bare
allusion to them and the plants on which they may be found. Some of them
may occur in one locality and some in another, and enough has perhaps
been said to enable any one to place any that he may find in the proper
genus, if not with the scientific name.
From the numerous instances we have met with of persons wholly
disinterested in the subject, collecting and making inquiries concerning
the bright orange patches next to be referred to, we are led to conclude
that most persons have, at least, seen them. These patches of
orange-coloured powder burst through the cuticle, and appear on the
young branches of wild roses, extending sometimes for two or three
inches in length Plate VII. fig. 147), and form one of the most
beautiful and obtrusive of the dust-like fungi. It is not confined to
roses; but the meadow-sweet, on which it is also found, does not grow in
localities where its parasite is so liable to meet the gaze of the
ordinary wayfarer. The habit of this rust is more or less that of those
which are associated with it. The pustules are not small and orbicular
as in most instances in other groups (except _Polycystis_), but are
large and irregular, and generally but few together or single. The
spores are variously coloured, and have peduncles, or footstalks, of a
greater or less length. In the rose rust these spores are profuse, but
the peduncle is short (Plate VII. fig. 148).
Plants of the pea and bean tribe are liable to be attacked by one of
these rusts, and in this instance the spores are so characteristic that
no one could well confound them with any other. Externally it appears as
an irregular brownish pustule, breaking through the epidermis and filled
with an impalpable powder, not unlike a pinch of “brown rappee” snuff.
The spores are ovoid, with a very long peduncle, whence its name
(_Uromyces appendiculata_). It appears on a great variety of plants, but
from the peculiarity of the spores Plate VII. fig. 150), is easily
recognized. Our figure represents it on the leaf of a vetch (Plate VII.
fig. 149). Almost at the commencement of this volume (Chap. III.) we had
occasion to refer in detail to some experiments made by De Bary on the
spores of this species. In the remarks then made occurs a recommendation
of reperusal, which would obviate any repetition here.
An allied species, and a beautiful one, is to be found on the stinking
iris (_Iris fœtidissima_), and another on the under surface of the
leaves of primroses.
The pilewort (_Ranunculus ficaria_) we have already seen attacked by one
species of microscopic fungi, and we have now to record the occurrence
of another. Some plants appear to be destined both alive and dead to
become the prey of others. The common nettle, for instance, as if in
retribution for the annoyance it often occasions on account of its
stinging propensities, has not less than twenty different species of
minute fungi, to say nothing of coleopterous and lepidopterous insects,
which make a home, sometimes upon its green leaves, and sometimes on its
dead stems. We might almost state that it has a flora and a fauna of its
own. The pilewort, too, has many foes; but these are fewer in number,
and mostly attack the living plant. The cluster-cups have been already
noticed; some do not fall within the limits of this volume, but one,
which is found in May and June, belongs to the present genus. It appears
like a purplish-brown powder bursting through blistered spots on the
leaves and footstalks Plate VII. fig. 156). The spores are small, and
are, of course, provided with pedicels Plate VII. fig. 157).
The under surface of the leaves of the white Dutch clover are often
sprinkled with black spots, which are nearly round and very numerous.
These are so many clusters of fungi belonging to a different section, in
which the threads are the important feature. But another parasite is
also found on leaves of the same plant, in which the pustules are far
less numerous and regular, and are often found on the petiole as well as
the leaf, distorting them and twisting them in various directions Plate
VII. fig. 154). This is the clover rust (_Uromyces apiculata_, Lev.),
which is a parasite on numerous plants, being found also on the great
water-dock and other kinds of dock. The spores are ovoid and brown, with
a short peduncle (Plate VII. fig. 155). A very beautiful species occurs
on the leaves of the ladies-mantle (_Alchemilla_), but hitherto we have
not been fortunate enough to collect it.
It can scarcely be too great an assumption to suppose that every one is
acquainted with the goat-willow (_Salix caprea_), or that every
schoolboy knows the birch (_Betula alba_). It may be proceeding a step
too far to affirm that all who know these trees well enough to
distinguish the one from the other, will have observed the under
surfaces of the leaves of both sprinkled with a golden dust, during the
summer months, and which are the spores of a parasitic fungus. So common
is this orange-coloured powder on leaves of the trees above-named, that
we can hardly believe any one to have had a branch of either in his hand
and not observed it, provided any leaves adorned the branch in question.
What this parasite is, and what its associates, it is our province to
endeavour to explain. Our figure (Plate VIII. fig. 160) represents a
leaf of the sallow or goat-willow, with the under surface exhibiting
yellow patches, consisting of spores, which are magnified in the next
figure (Plate VIII. fig. 161). This exceedingly common rust is termed
_Lecythea caprearum_, Lev., when in the condition figured; but in
reality this is only the summer stage, bearing the summer fruit of
_Melampsora salicina_, which latter attains its mature development on
the same leaves in the succeeding winter (Plate IX. fig. 191) or early
spring. Of course this latter remark applies to the fallen leaves, for
at this period all the willows and other deciduous trees are bare. But
the leaves, before they fall, give evidence of the parasite at work; and
if the collected decaying mass of rubbish at the base of sallow bushes
be examined about March, these leaves will be found bearing upon them
mature heaps of elongated, wedge-shaped spores, closely packed side by
side (Plate IX. fig. 192), and which, whilst still adherent, may often
be found in active germination, as represented in an allied species at
the bottom of our plate (Plate IX. fig. 197). This phenomenon consists
in the production of cylindrical tubes, more or less elongated, from the
upper extremity (rarely from the base) of the prismatic spores. These
tubes are straight or twisted, simple or forked, and each of them
becomes divided by transverse septa into four unequal cells towards
their apex, from each of which is produced a spicule bearing a
sporidium, or spherical secondary fruit, in the same manner as in the
genera _Puccinia_ and _Aregma_. It should be observed, that the winter
spores of this rust are borne on the opposite surface of the leaves to
the summer spores: for whilst the latter are developed from the under
surface, the former are found on the upper. This being also an instance
of di-morphism, the summer condition, when spherical spores are
produced, should not be regarded as a distinct plant, and the name of
_Lecythea caprearum_ does not merit retention in the list of fungi.
There are five species of this interesting group, or genus, found in
Great Britain, to the residue of which we may only briefly allude. It
has already been stated that, in summer, the yellow spores of a rust are
found on the under surface of birch-leaves. These must be sought on the
young twigs or suckers, proceeding from the stumps of trees which have
been cut down: pale discoloured spots on the upper surface of the leaves
indicate the presence of the rust beneath. This is the _Uredo betulina_
of old authors (begging their pardons, for some of them still live), the
_Lecythea longicapsula_ of more recent times, and the summer spores of
_Melampsora betulina_, according to M. Tulasne and his disciples. When
fresh, it is reputed to exhale a faint odour, as of the primrose. During
the winter and spring months the wedge-like spores of the second crop
are matured on the fallen leaves (Plate IX. figs. 189, 190), and these
are capable of a speedy germination, and the production of secondary
reproductive bodies, as in the willow rust above alluded to.
Probably, also, the similar rust on the poplar (Plate IX. figs. 195,
196), or on the aspen, may be met with under like conditions; _i.e._,
the summer spores, which are yellow and spherical, on the living leaves,
and the brown permanent masses of winter spores on the fallen and
decaying leaves. The sole remaining British species is not uncommon on
leaves of the common spurge in gardens, and whilst the yellow
pulverulent spores occur on the upper, it will not be improbable that
black permanent spots will be found on the lower leaves (Plate IX. figs.
193, 194), enclosing closely-packed, rudimentary, elongated or
wedge-shaped cellules of the winter spores.
Any one may make himself acquainted with the genus _Coleosporium_ with
but little trouble, which the acquisition will more than compensate. A
summer stroll into any locality in which the common coltsfoot can be
found, will be certain to prove sufficient. Let the spot selected be any
station on the North Kent Railway, for those who reside in town, or even
a trip to the Crystal Palace and a stroll in the grounds, and when the
well-known leaves of the coltsfoot are descried, the under surface of
the first leaf will doubtless give proof of the presence of the fungus
in question, by the orange spores amongst its dense woolly hairs.
Sometimes the leaf is almost covered beneath with the bright
orange-coloured dust. This is the coltsfoot rust (_Coleosporium
tussilaginis_, Lev., Plate VIII. fig. 180), which may serve as a type of
the rest. It may be observed that a species of cluster-cup, or
_Æcidium_, with spores of nearly the same colour, is also to be found on
the leaves of the same plant; but in this case the upper surface of the
leaf has also corresponding purplish spots, and, what is of still more
importance, the spores are seated in small fringed cups. The rust is
common till the wintry frosts have set in, and is far more conspicuous
than the cluster-cups. A kind of di-morphism prevails in all the species
of this genus. Some of the pustules resolve themselves into a kind of
powder, whilst others remain entire and solid. Generally there is the
largest proportion of globose, dust-like, free spores, produced in the
earliest developed fungi, whilst they become more rare towards the close
of the season. The permanent spore-spots consist of obovate cellules
placed side by side, each of which is divided transversely by three or
four septa, and is filled with an orange-red endochrome (Plate VIII.
fig. 181); the exterior being enveloped in a kind of mucous layer. The
arrangement of spores when packed together in the pustule is shown in
Plate VIII. fig. 182, from an allied species. When these spores
germinate, which they do with great readiness, each division emits a
long tube, which generally remains simple and undivided, and from its
extremity is produced a reproductive body of an obovate or nearly
kidney-shape. These filaments are about 1/120th of an inch in length, of
a colourless transparent membrane, along which the orange-red contents
of the spores pass into the newly-formed sporidia, or reproductive
bodies by which they are terminated. Most of these reniform sporidia
disengage themselves from the filaments on which they are produced, and
either elongate themselves into a simple and uniform filament, or swell
at the extremity as if to reproduce a second spore. If the newly-formed
sporidia do not become free, they increase the length of their primitive
filament, which by a frequent repetition of the process becomes a tube
swelling out at unequal distances.
[Illustration:
Plate X.
W. West imp.
]
The summer spores, or pulverulent spores of the first generation, which
are analogous to the Uredospores of _Aregma_, are also capable of
germination, for, if placed in favourable circumstances, they will
develop very long filiform processes, which either remain simple or
become more or less branched, but always nearly uniform in their
diameter. M. Tulasne states that he has observed this germination many
times, though we have been less fortunate.
Of the six species of this genus known to occur in Great Britain, the
majority may be commonly met with. That very widely-diffused plant, the
wood cow-wheat (_Melampyrum pratense_), known well to all amateur
botanists for its pertinacity in drying black, and presenting anything
but an inviting appearance to claim for it a place in the herbarium—also
becomes the matrix for the development of a member of this genus;
_i.e._, the cow-wheat rust (_Coleosporium Rhinanthacearum_, Lev.), and
which is found on other allied plants, as the little eyebright
(_Euphrasia officinalis_), &c. (Plate VIII. fig. 176). In colour and
habit it resembles the last-named species, and its free, echinulate
spores (Plate VIII. fig. 177) form a pretty object for the microscope.
Another equally common species is found inhabiting the leaves of the
sow-thistles (_Sonchus arvensis_ and _S. oleraceus_), and in the autumn
may generally be found on either of those plants, presenting the
appearance delineated in our plate (Plate VIII. fig. 178). The permanent
spores resemble in many points those of the first species, as will be
seen from the figure from De Bary’s treatise on this subject (Plate
VIII. fig. 179). This is certainly one of the most showy of uredinous
fungi, and could not be well overlooked.
The butter-bur rust (_Coleosporium petasites_, Lev.) and the Campanula
rust (_Coleosporium Campanulæ_, Lev.) are found, the former on the
leaves of the butter-bur, and the latter on those of the harebell and
other _Campanulæ_, less frequently. We have, however, indicated
sufficient, since their great similarity in unprofessional eyes will
furnish, in one or two species, all that is desirable for the
microscopist.
Unless some similar plan to the following be adopted for examining the
species of this genus, it may result in disappointment; for the slight
attachment of the joints to each other will otherwise present only a
mass of simple echinulate cellules, if a portion be only removed from
the leaf on the point of a lancet. This method consists in making a thin
vertical section of a pustule in which the spores are contained; by this
means the arrangement of the fruit and the mucedinous threads from
whence they proceed may be observed. Any person possessed of the
cardinal virtues of microscopy—patience and perseverance—will be
rewarded in this instance; whilst those who are deficient will lose an
object worthy of the virtues they dare not boast. But few instances have
occurred in this and the preceding chapters in which the exercise of any
great ingenuity or application has been called for; the most juvenile or
truest tyro at the microscope may see for himself much of what has been
indicated, whilst a few opportunities have occurred for more practised
manipulists to prove that they are neither juveniles nor tyros.
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