_MILDEW AND BRAND._
DR. WITHERING’S “Arrangement of British Plants” in 1818 reached its
sixth edition. This is less than half a century ago, and yet the whole
number of species of Fungi described in that edition was only 564, of
which three hundred were included under the old genus _Agaricus_. Less
than eighty of the more minute species of Fungi, but few of which
deserve the name of microscopic, were supposed to contain all then known
of these wonderful organisms. Since that period, microscopes have become
very different instruments, and one result has been the increase of
Withering’s 564 species of British Fungi to the 2,479 enumerated in the
“Index Fungorum Britannicorum.” By far the greater number of species
thus added depend for their specific, and often generic characters, upon
microscopical examination. The proportion which the cryptogamic section
bears to the phanerogamic in our local Floras before 1818, now almost
involuntarily causes a smile. Even such authors as were supposed to pay
the greatest possible respect to the lower orders of plants could never
present an equal number of pages devoted to them, as to the higher
orders. Relhan, for instance, only occupies one-fifth of his “Flora
Cantabrigiensis,” and Hudson one-fourth of his “Flora Anglica,” with the
Cryptogamia. At the present time, it will be seen that, with a liberal
allowance for “hair-splitting,” the number of British species of
flowering plants scarcely exceeds three-fourths of the number of Fungi
alone, not to mention ferns, mosses, algæ and lichens, and yet we have
no “Flora” which contains them, and but a minority of our botanists know
anything about them. If we need excuse for directing attention to some
of the most interesting of these plants, let the above remarks suffice
in lieu of formal apology.
“Mildew” is just one of those loose terms which represent no definite
idea, or a very different one to different individuals. Talk of _mildew_
to a farmer, and instantly he scampers mentally over his fields of
standing corn in search of the brown lines or irregular spots which
indicate the unwelcome presence of _Puccinia graminis_, known to him,
and to generations of farmers before him, as “mildew.” Try to convince a
Norfolk farmer that anything else is “mildew,” and he will consider you
insane for your pains. Speak of _mildew_ in your own domestic circle,
and inquire of wives, or daughters, or servants, what it means, and
without hesitation another, and even more minute species of fungus,
which attacks damp linen, will be indicated as the true mildew, to the
exclusion of all others; and with equal claims to antiquity. Go to
Farnham, or any other hop-growing district, and repeat there your
question,—What is _mildew_?—and there is every probability that you will
be told that it is a kind of mould which attacks the hop plant, but
which differs as much from both the mildew of the farmer and the
laundry-maid as they differ from each other. The vine-grower has his
mildew, the gardener his mildewed onions, the stationer his mildewed
paper from damp cellars, the plasterer his mildewed walls, and in almost
every calling, or sphere in life, wherever a minute fungus commits its
ravages upon stock, crop, or chattels, to that individual owner it
becomes a bug-bear under the name of “mildew.” Reluctantly this vague
term has been employed as a portion of the title to this chapter, but it
must be limited in its application to the “mildew of corn,” known to
botanists as _Puccinia graminis_, and _not_ to include the numerous
other microscopic Fungi to which the name of _mildew_ is often applied.
The origin of this term and its true application may undoubtedly be
traced to _mehl-thau_, “meal dew.” A singular proof of the ignorance
which prevails in regard to all the fungal diseases of corn, may be
found in the fact that at least one of our best etymological
dictionaries states that the _mildew_ in corn is the same as the _ergot_
of the French. Had the writer ever been a farmer, he would have known
the difference; had he ever seen the two, he could scarcely have made
such a mistake. It is barely possible for him ever to have heard the
ergot of grain called by the name of _mildew_.
How long this disease has been known, is an unsolved problem. About the
middle of the last century a tract was published on this subject in
Italy, but this was probably not even the first intimation of its
fungoid character. Before such conclusion had been arrived at, men may
have struggled in the dark, through many generations, to account for a
phenomenon with which they were doubtless familiar in its effects. In
1805, Sir Joseph Banks published his “Short Account,” illustrated by
engravings from the inimitable drawings of Bauer, whereby many in this
country learnt, for the first time, the true nature of _mildew_.
[Illustration:
Plate III.
W. West imp.
]
With a view to the clearer understanding of these parasites in the
phases of their development, let us select one, and we cannot do better
than adhere to that of the wheat and other graminaceous plants. A fine
day in May or June dawns upon our preparations for a stroll, far enough
into the country to find a wheat-field. Even now, with the area of the
metropolis constantly widening, and banishing farmers and wheat fields
farther and farther from the sound of Bow-bells, a corn field may be
reached by a good stiff walk from Charing-Cross, or a six-penny ride at
the most, in nearly any direction. Having reached the field, it may be
premised that a walk into it of less than twenty yards will be sure to
reward you with the fungus we are in quest of. Look down at the green
leaves, especially the lower ones, and you will soon find one apparently
grown rusty. The surface seems to be sprinkled with powdered red ochre,
and grown sickly under the operation. Pluck it carefully, and examine it
with a pocket lens. Already the structure of a healthy leaf is familiar
to you, but in the present instance the cuticle is traversed with
numerous longitudinal cracks or fissures, within which, and about their
margins, you discern an orange powder, to which the rusty appearance of
the leaf is due. Further examination reveals also portions in which the
cuticle is distended into yellowish elongated pustules, not yet
ruptured, and which is an earlier stage of the same disease. This is the
“rust” of the agriculturist, the _Trichobasis rubigo-vera_ of botanists,
the first phase of the corn mildew.
To know more of this parasite, we must have recourse to the microscope;
having therefore collected a few leaves for this purpose, we return
homewards to follow up the investigation. We will not stay to detail the
processes of manipulation, since these will not offer any deviation from
the ordinary modes of preparation and examination of delicate vegetable
tissues.
The vegetative system of the “rust,” and similar fungi, consists of a
number of delicate, simple, or branched threads, often intertwining and
anastomosing, or uniting one to the other by means of lateral
branchlets. These threads, termed the mycelium, penetrate the
intercellular spaces, and insinuate themselves in a complete network,
amongst the cells of which the leaf, or other diseased portion of the
plant, is composed. High powers of the microscope, and equally high
powers of patience and perseverance, are necessary to make out this part
of the structure. We may regard the whole mycelium of one pustule, or
spore-spot, as the vegetative system of one fungal plant. At first this
mycelium might have originated in a number of individuals, which
afterwards became confluent and combined into one for the production of
fruit, that is to say, an indefinite number of points in the vicinity of
the future mycelium developed threads; and these, in the process of
growth, interlaced each other, and ultimately, by means of transverse
processes, became united into one vegetative system, in which the
individuality of each of the elementary threads became absorbed, and by
one combined effort a spore-spot, or cluster of fruit, was produced. In
the first instance a number of minute, transparent, colourless cellules
are developed from the mycelium: these enlarge, become filled with an
orange-coloured endochrome, and appear beneath the cuticle of the leaf
as yellowish spots. As a consequence of this increase in bulk, the
cuticle becomes distended in the form of a pustule over the yellow
cellules, and at length, unable longer to withstand the pressure from
beneath, ruptures in irregular, more or less elongated fissures (Plate
VII. fig. 141), and the yellow bodies, now termed _spores_ (whether
correctly so, we do not at present inquire), break from their short
pedicels and escape, to the naked eye presenting the appearance of an
orange or rust-coloured powder. In this stage the spores are globose, or
nearly so, and consist of but one cell Plate VII. figs. 142, 144). It
will afford much instructive amusement to examine one of these ruptured
pustules as an opaque object under a low power, and afterwards the
spores may be viewed with a higher power as a transparent object. The
difference in depth of tint, the nearly colourless and smaller immature
spores, and the tendency in some of the fully matured ones to elongate,
are all facts worthy of notice, as will be seen hereafter.
A month or two later in the season, and we will make another trip to the
cornfield. Rusty leaves, and leaf-sheaths, have become even more common
than before. A little careful examination, and, here and there, we shall
find a leaf or two with decidedly brown pustules intermixed with the
rusty ones, or, as we have observed several times during the past
autumn, the pustules towards the base of the leaf orange, and those
towards the apex reddish-brown. If we remove from the browner spots a
little of the powder, by means of a sharp-pointed knife, and place it in
a drop of water or alcohol on a glass slide, and after covering with a
square of thin glass, submit it to examination under a quarter-inch
objective, a different series of forms will be observed. There will
still be a proportion of subglobose, one-celled, yellow spores; but the
majority will be elongated, most with pedicels or stalks, if they have
been carefully removed from the leaf, and either decidedly two-celled,
or with an evident tendency to become so. The two cells are separated by
a partition or dissepiment, which divides the original cell transversely
into an upper and lower cell, with an external constriction in the plane
of the dissepiment (Plate IV. fig. 59). These bilocular or two-celled
spores are those of the “corn mildew” (_Puccinia graminis_), which may
be produced in the same pustules, and from the same mycelium, as the
“corn rust,” but which some mycologists consider to be a distinct
fungus, others only a modification or stage of the same fungus. After an
examination of the different forms in the allied genera to which these
chapters are devoted, we shall be able with less of explanation and
circumlocution to canvass these two conflicting opinions.
Let us proceed, for the third and last time, to our cornfield, when the
corn is nearly or fully ripe, or let us look over any bundle of straw,
and we shall find blackish spots, from the size of a pin’s head to an
inch in length, mostly on the sheaths of the leaves, often on the culm
itself. This is the fully developed _mildew_, and when once seen is not
likely afterwards to be confounded with any other parasite on straw
(fig. 57). The drawings of Bauer have already been alluded to. Bauer was
botanical draughtsman to George III., and his exquisite drawings, both
of the germination of wheat and the fungi which infest it, are marvels
of artistic skill. A reduced figure from part of one of his drawings is
given (Plate IV. fig. 58), exhibiting a tuft of the bilocular spores of
_Puccinia graminis_ bursting through a piece of wheat straw. These
closely-packed tufts or masses of spores, when examined with a common
lens, seem, at first, to resemble the minute sorus of some species of
fern; but when seen with higher powers, the apparent resemblance gives
place to something very different. The tufts consist of multitudes of
stalked bodies, termed spores, which are constricted in the middle and
narrowed towards either extremity. The partition, or septum, thrown
across the spore at the constriction, separates it into two portions,
each of which consists of a cell-wall enclosing an inner vesicle filled
with the endochrome (fig. 59) or granular contents, in which a nucleus
may often be made out. This species of _Puccinia_ is very common on all
the cereals cultivated in this country, and on many of the grasses. A
variety found on the reed was at one time considered a distinct species;
but the difference does not seem sufficient to warrant a separation.
However near some other of the recognized species may seem to
approximate in the form of the spores, a very embryo botanist will not
fail to observe the distinctive features in the spores of the corn
mildew, and speedily recognize them amongst a host of others; subject,
as they may be, to slight deviations in form, resulting either from
external pressure, checks in development, or other accidental
circumstances, or the variations of age.
There is no doubt in the minds of agriculturists, botanists, _savans_,
or farm-labourers, that the mildew is very injurious to the corn crop.
Different opinions may exist as to how the plants become inoculated, or
how infection may be prevented or cured. Some have professed to believe
that the spores, such as we have seen produced in clusters on wheat
straw, enter by the stomata, or pores, of the growing plant, “and at the
bottom of the hollows to which they lead they germinate and push their
minute roots into the cellular texture.” Such an explanation, however
plausible at first sight, fails on examination, from the fact that the
spores are too large to find ingress by such minute openings. It is
improbable that the _spores_ enter the growing plant at all. The
granular contents of the spores may effect an entrance either through
the roots or by the stomata, or the globose bodies produced upon the
germination of the spores may be the primary cause of infection. We are
not aware that this question has been satisfactorily determined. It is
worthy of remembrance by all persons interested in the growth of corn,
that the mildew is most common upon plants growing on the site of an old
dunghill, or on very rich soil. As the same _Puccinia_ is also to be
found on numerous grasses, no prudent farmer will permit these to
luxuriate around the borders of his fields, lest they should serve to
introduce or increase the pest he so much dreads.
The germination of the spores of the corn mildew is a very interesting
and instructive process, which may be observed with a very little
trouble. If the spores be scraped from the sori of the preceding year
(we are not sure that those of the current year will succeed), and kept
for a short time in a damp atmosphere under a glass receiver, minute
colourless threads will be seen to issue both from the upper and lower
divisions of the spores. These will attain a length several times that
of the spores from whence they spring. The extremities of these threads
ultimately thicken, and two or three septæ are formed across each,
dividing it into cells, in which a little orange-coloured endochrome
accumulates. From the walls of each of these cells, or joints, a small
pedicel, or spicule, is produced outwards, the tip of which gradually
swells until a spherical head is formed, into which the orange-coloured
fluid passes from the extremities of the threads.[4] A quantity of such
threads, bearing at their summits from one to four of these
orange-coloured, spherical, secondary fruits, supply a beautiful as well
as interesting object for the microscope. When matured, these globose
bodies, which Tulasne has called _sporidia_, fall from the threads, and
commence germinating on their own account. It is not impossible that the
sporidia, in this and allied genera, may themselves produce a third and
still more minute fruit, capable of diffusion through the tissues of
growing plants, or gaining admission by their stomata. Nothing of the
kind, however, has yet been of certainty discovered.
Footnote 4:
Similar in all essential particulars to the germination of _Aregma_
(Plate III. fig. 45).
Forty other species of _Puccinia_ have been recorded as occurring in
Great Britain, to all of which many of the foregoing remarks will also
apply—viz., such as relate to their two-celled spores being found
associated with, and springing from, the same mycelium as certain
orange-coloured one-celled spores; and also the main features of the
germinating process.
[Illustration:
Plate IV.
W. West imp.
]
A very singular and interesting species is not uncommon on the more
delicate grasses, being found chiefly confined to the leaves, and
produced in smaller and more rounded, or but slightly elongated, patches
(Plate IV. fig. 60). We have met with it plentifully amongst the turf
laid down in the grounds of the Crystal Palace at Sydenham, and also on
hedge-banks and in pastures. The spores are rather smaller than those of
_Puccinia graminis_, but, like them, much elongated, slightly
constricted, and borne on persistent peduncles. The most prominent
distinction may be found in the apices of the spores, which, in this
instance, are not attenuated, but crowned with a series of little
spicules, or teeth, whence the specific name of _coronata_ has been
derived (Plate IV. fig. 62).
The Labiate family of plants and its ally the Scrophulariaceæ are also
subject to the attacks of several kinds of Brand, a name, by the bye,
often applied locally to the corn mildew and other similar parasites,
and which may have originated in the scorched or _burnt_ appearance
which the infected parts generally assume. In the former natural order
the different kinds of mint, the ground-ivy, the wood-sage, and the
betony, and in the latter, the water figwort and several species of
veronica, or speedwell, are peculiarly susceptible; and on most a
distinct species of _Puccinia_ is found. To provide against doubt which
the less botanical of our readers may possess of the meaning or value of
the term _Puccinia_, which has already occurred two or three times in
this chapter, a brief explanation may be necessary, which more
scientific readers will excuse.
In botany, as in kindred sciences, acknowledged species have their
trivial, or specific name, generally derived from the Latin. In the last
species referred to, this was _coronata_, meaning _crowned_, in
reference to the coronated apex of the fruit. Any indefinite number of
species with some features in common are associated together in a group,
which is termed a _genus_, and the term prefixed to the specific name of
each species constituting that genus is its generic name, also commonly
derived from the Latin or Greek. In this instance it is _Puccinia_,
derived from the Greek _puka_, meaning _closely packed_, singularly
applicable to the manner in which the spores are packed together in the
pustules. The common features, or generic distinctions, of this genus,
are uniseptate spores borne on a distinct peduncle.
In returning to the species found on Labiate plants, let us suppose
ourselves to have strolled towards Hampstead Heath, and south of the
road leading from Hampstead to Highgate, near certain conspicuous and
well-known arches, built for a purpose not yet attained, are two or
three muddy ponds nearly choked up with vegetation. Some fine autumnal
afternoon, we must imagine ourselves to have reached the margin of the
most northern of these ponds, and amidst a thick growth of reeds,
sedges, and other water-loving plants, to have found the water-mint in
profusion and luxuriance, with every leaf more or less occupied, on its
under surface, with the yellow spores of a species of rust
(_Trichobasis_) mixed with the browner septate spores of the mint brand
(_Puccinia Menthæ_). This is common also on the horse-mint and
corn-mint; we have found it on the wild basil and wild thyme, and once
only on marjoram. Having collected as many leaves as we desire, and
returned to home and the microscope, we proceed to examine them in the
same manner as we have already examined the mildew, and as a result of
such proceeding arrive at the following conclusions:—The pustules are
small and round, never elongated as in the corn mildew, and generally
confined to the under surface of the leaves (Plate IV. fig. 69). The
spores are subglobose, slightly constricted, and the two cells nearly
two hemispheres, with their flat surfaces turned towards each other
(fig. 70). The form delineated in figure 75 is that of the sorus of many
of the epiphytal brands, the centre being occupied by the closely-packed
spores, surrounded to a greater or less extent by the remains of the
ruptured epidermis.
Although the species of Puccinia (_P. glechomatis_) found on the leaves
of the ground-ivy is said to be very common, we sought it in vain
amongst every cluster of that plant met with during last summer and
autumn, until, nearly despairing of finding it at all, we at last
encountered a plot of ground-ivy covering the ground to the width of two
or three yards, and in length eight or ten, nearly every plant being
attacked by the _brand_. This was in the corner of a pasture, and the
only time we found infected plants. The fungus, however, may be as
common as the plant in other localities. The pustules on the leaves are
larger than those of the mints, and also confined to the inferior
surface (fig. 73). The spores are elliptic and but slightly constricted;
the apex is often pointed, though not always so much as in our figure
(fig. 74).
Of other species found on allied plants we have not considered it
necessary to give figures, or write much. The betony brand (_P.
Betonicæ_, DC.) does not seem to be common enough to be readily found by
any one desiring to examine it for himself; and the same may be said of
the figwort brand (_P. Scrophulariæ_, Lib.), the wood-sage brand (_P.
Scorodoniæ_, Lk.), and the speedwell brand (_P. Veronicarum_, DC.); all
of these are, however, characterized by a distinct feature, or features,
which have been considered of sufficient importance to constitute a
separate species.
We have had occasion to refer incidentally to the brand found on the
under surface of the leaves of the wood-anemone (_P. Anemones_, P.).
This is one of the earliest and commonest species. Go wherever the
wood-anemone abounds, in any of the woods lying immediately to the north
of the metropolis, or any of the woods in Kent, and from March to May it
will not be difficult to find attenuated, sickly-looking leaves, with
the under surface covered with the pustules of this brand, looking so
like the sori of some fern (fig. 65) that it _has_ been, and still _is_,
sometimes considered as such. In Ray’s “Synopsis” (3rd edition, 1724),
it is described in company with the maidenhair and wall-rue ferns; a
figure is given of it in the same work (t. iii. fig. 1), and it is
stated,—“this capillary was gathered by the Conjuror of Chalgrave.”
When, afterwards, it was better understood, and the spots came to be
regarded as true parasitic fungi, it still for a long time continued to
bear the name, not even yet quite forgotten, of the Conjuror of
Chalgrave’s fern.
An examination of the spores, both collectively in the pustules, and
separately under a high power, will not fail to convince any one who has
examined only the species we have already alluded to, that this parasite
on the anemone (_P. Anemones_) is a true _Puccinia_, and a most
interesting one. The two cells of the spores are nearly spherical, and
the constriction is deeper and more positive than in any of the
preceding. Moreover, the surface of the spore is minutely and
beautifully echinulate, or covered with erect spines (Plate IV. fig.
66). Some few other of the species found in Britain have echinulate
spores, but those are not common like the present. One word of caution
to the amateur in search of the _Puccinia_ on the anemone. It will be
fruitless looking for it on the large foliaceous bracts of the
flower-stalk, since these may be turned up carefully, till the back
aches with stooping, ere a solitary pustule will be found; but the true
leaves, proceeding from the rhizomes, are certain soon to afford you
specimens.
Everybody knows the dandelion, but it is not every one who has noticed
the fungi found upon its leaves. These are most commonly of two kinds,
or probably the unilocular and bilocular forms of the same species: the
latter we have found in the month of May, and the former in August and
September. The lower leaves of young seedlings have generally rewarded
us with the best specimens of the septate-fruited brand (_Puccinia
variabilis_, Grev.). The pustules occur on both sides of the leaf, and
are very small and scattered (fig. 82). The spores are singularly
variable in form: sometimes both divisions are nearly equal in size;
sometimes the upper, and sometimes the lower, division is the smallest;
occasionally the septum will be absent altogether; and more rarely, the
spores will contain three cells. From the very variable character of the
spores (fig. 83), the specific name has been derived.
No species in the entire genus makes so prominent an appearance as the
one found on the radical leaves of the spear thistle (_Carduus
lanceolatus_). This latter plant is exceedingly abundant, and so is its
parasite (_Puccinia syngenesiarum_, Lk.). From the month of July till
the frosts set in we may be almost certain of finding specimens in any
wood. The leaves have a paler roundish spot, from one-twelfth to
one-fourth of an inch in diameter, on the upper surface, and a
corresponding dark brown raised spot on the under surface, caused by an
aggregation of pustules, forming a large compound pustule, often partly
covered with the epidermis. The individual pustules are small, but this
aggregate mode of growth gives the clusters great prominence, and
therefore they are not easily overlooked (Plate IV. fig. 63). Although
not confined to this species of thistle, we have not yet found this
_Puccinia_ on any other plant. The spores are elliptical, rather
elongated, constricted, and without spines (fig. 64).
Other species of _Puccinia_ are found on Composite plants, but with none
of these is the present fungus likely to be confounded, if regard be had
to its peculiar habit. The leaves, for instance, of the common knapweed
(_Centaurea nigra_) are often sprinkled with the small pustules of the
centaury brand (_Puccinia compositarum_, Sch.); these generally occupy
the under surface of the lower radical leaves (fig. 67); occasionally a
few of the pustules appear on the upper surface. We have not often found
this fungus in the neighbourhood of London on the leaves of the
knapweed, but, on the other hand, we have encountered it very commonly
on those of the saw-wort (_Serratula tinctoria_). The spores are oval,
scarcely constricted, and not attenuated in either direction (fig. 68).
Other Composite plants than those above named are liable to attacks from
this parasite.
In our school-days we remember to have spent many a stray half-hour
digging for “earthnuts,” under which name we, as well as our elders and
betters, knew the tubers of _Bunium flexuosum_. Not then, nor for many
years after, did we notice, or regard if we did notice, the distorted
radical leaves and leaf-stalks, and the blackish-brown spots, which
reveal the cause in the presence of a brand, or parasitic fungus, of
this genus (_Puccinia Umbelliferarum_, DC.), which is extremely common
on this, as well as some other allied plants. If any spot is searched
where this plant grows in any profusion, before the flowering stalks
have made their appearance above the surrounding grass, this _Puccinia_
will be readily found by the twisted, contorted, sickly appearance of
the infested leaves (fig. 71), the petioles of which are often swollen
and gouty in consequence. The sporidia are shortly stalked, and
generally very much constricted (fig. 72). The species found on the
stems of the hemlock, and also that on Alexanders (_Smyrnium
Olusatrum_), are distinct; the spores of the latter being covered with
tubercles or warts (figs. 55, 56). During a botanical ramble through
Darenth Wood in April of the year just passed away, in some parts of
which the sanicle abounds, we found the bright glossy leaves of this
singular and interesting plant freely sprinkled with the pustules of a
_Puccinia_ (_P. Saniculæ_, Grev.), which is not at all uncommon on this,
but has not hitherto been found on any other plant. Dr. Greville, of
Edinburgh, was the first to describe this, as well as many other of our
indigenous minute Fungi. For many years he has toiled earnestly and
vigorously at the lower cryptogams, as evidenced by his “Scottish
Cryptogamic Flora,” published in 1823; and yet his continual additions
to the records of science show him to be earnest and vigorous still.
We have by no means exhausted the catalogue of Fungi belonging to this
genus found in Britain, nor even those commonly to be met with; but the
fear of prolixity, and the desire to introduce a description of other
forms into the space still remaining to us, prompt us to dismiss these
two-celled brands with but a brief allusion to such as we cannot
describe. Box-leaves are the habitat of one species, and those of the
periwinkle (Plate VI. fig. 132) of another. One vegetates freely on the
leaves of violets through the months of July and August, and another
less frequently on the enchanter’s nightshade. Several species of
willow-herb (_Epilobium_) are attacked by one _Puccinia_ (Plate IV.
figs. 78, 79), and a single species by another. Plum-tree leaves,
bean-leaves, primrose leaves, and the half-dead stems of asparagus, have
their separate and distinct species, and others less commonly attack the
woodruff, bedstraw (Plate VIII. figs. 172, 173), knotgrass, ragwort, and
other plants less common, more local, or, to the generality of the
non-botanical, but imperfectly known.
We have found, not uncommonly in the autumn, the scattered pustules of a
brand on the stems and leaves of the goat’s-beard, occupying the places
which were scarred with the remains of cluster-cups that had flourished
on the same spots a month or two previously (Plate IV. fig. 76). The
pustules are by no means minute, but elongated and bullate; the spores
beautifully studded with warts (Plate IV. fig. 77). This species cannot
certainly be identical with _Puccinia compositarum_ (Schlecht), _P.
syngenesiarum_ (Lk.), or _P. tragopogonis_ (Corda). In none of these do
the spores appear to be warted, and the habits of both the latter are
different. Its nearest associate appears to be _P. centauriæ_ (Corda),
at least in the fruit, and whilst the form and character of these organs
are considered of any value in the determination of species, smooth
spores cannot be associated, we think, with tuberculate or echinulate
spores under the same name.
In the spores of the species to which attention has been more specially
directed we have types of the principal forms. In the “corn-mildew” they
are elongated, and tapering towards either end; in the “coronated brand”
the apex is crowned with spicular processes; in the “wind-flower brand”
the entire spores are echinulate; in the “mint brand” they are globose;
in the “composite brand” elliptic; in the “earth-nut brand,” nearly cut
in two at the septum; and in the “dandelion brand,” so variable in form
that no two are precisely alike. On the other hand, all are
characterized by a transverse septum dividing each spore into two cells.
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