_COMPLEX BRANDS._
FROM the twin-spored genus we pass to another, in which the spores are
usually divided into three cells, and which, from this cause, has been
named _Triphragmium_. Only one species has hitherto been found in this
country, and _that_ not very commonly, on the leaves of the
meadow-sweet, _Spiræa ulmaria_ (Plate III. fig. 47). Externally, it much
resembles, in the size and character of the pustules, many of the
above-named brands, but when seen under the microscope this similarity
disappears. In general outline the spores are nearly globose, and
externally papillose. In one species, found on the Continent, but not
hitherto in Great Britain, the spores are covered with curious
long-hooked spines, by means of which they adhere tenaciously to each
other. In germination, the spores of _Triphragmium_ do not offer any
noteworthy deviation from those of _Puccinia_,[5] and the chief interest
of our indigenous species lies in the three-celled form of its spores
(fig. 48), to which occasionally those of _Puccinia variabilis_
approximate, and may be regarded as the link which unites the two
genera.
Footnote 5:
Mr. Currey has only seen the tips of the germinating threads swell,
and become septate, each of the joints thus formed falling off and
germinating without producing spherical sporidia; whilst Tulasne
figures globular sporidia, as will be seen in our fig. 49, reduced
from the figure by Tulasne.—(_Vide_ Currey, in “Quarterly Journal of
Microscopical Science,” 1857, pp. 117, &c.)
The old story of “Eyes and no Eyes” is too often literally true, not
only with the children it was written to amuse and instruct, but also
with children of a larger growth who scorn such baby tales, and disdain
such baby morals. Out of more than a thousand indigenous species of
microscopic fungi, of which there is generally some evidence afforded of
their presence visible to the naked eye, how few are there of the
millions that inhabit our island who can count twenty species that they
have ever seen; still fewer that have noticed one hundred. Amongst the
twenty species known to the few will probably be included one which
appears in autumn in prominent black spots, the size of a large pin’s
head, or half a turnip seed, with the flat face downwards, sprinkling
the under surface of blackberry leaves (fig. 39); with larger, reddish,
purplish, or reddish-brown spots on the upper to indicate the presence
of the fungus beneath. Just at the time when blackberries are ripe,
these spots are in perfection on the leaves, and _their_ eyes must have
been sadly at fault who could ever have gathered their own blackberries
without seeing the discoloured leaves. The coloured spots on the face of
the leaf are due to the diseased state of the tissues caused by the
parasite on the opposite surface. As much of the leaf as contains two or
three of the black pustules should be removed carefully with a knife or
sharp scissors, and submitted to microscopical examination; each will be
seen to consist of a dense tuft of blackish, elongated, stalked bodies,
clustered as in fig. 44, but much more numerously and closely packed
together. These are the spores of the blackberry brand (_Aregma
bulbosum_, Fr.). A few of these spores should be removed on the point of
a sharp penknife, placed on a glass slide with a drop of distilled water
or alcohol, covered with thin glass, and then viewed with a quarter-inch
objective. Each spore has a stalk longer than itself, thickened below,
and containing a yellow granular core. The spore itself is much longer
than in any of the _Pucciniæ_, of a dark brown colour, and apparently
divided by several transverse partitions into three, four, or more
cells, the whole surface being covered with minute warts or prominences
(Plate III. fig. 41).
In 1857, Mr. F. Currey investigated the structure of these spores, and
the results of these experiments were detailed in the “Quarterly Journal
of Microscopical Science.” One conclusion arrived at was, that “the idea
of the fruit consisting of sporidia united together and forming a chain,
is certainly not in accordance with the true structure. The sporidia are
not united to one another in any way, but, although closely packed for
want of space, they are in fact free in the interior of what may be
called a sporangium or ascus.” To arrive at this conclusion, careful
examination was necessary, and new modes of manipulation essential. The
details of one method employed were to the following effect:—A
sufficient number of spores were removed on the point of a lancet, and
placed on a slide in a drop of alcohol. Before the spirit was quite
evaporated, two or three drops of strong nitric acid were added, and the
whole covered with thin glass. The slide was then warmed over a
spirit-lamp, the acid not being allowed to boil, but only gradually
heated to boiling point. By this means the fruit was found to consist of
an outer membrane, nearly transparent, and studded with tubercles; that
this membrane enclosed a number of cells which constituted the apparent
joints, and which were naturally flattened at either end by mutual
pressure. When the outer membrane was dissolved or ruptured, these cells
escaped, and became detached from each other. The cells, thus set free,
exhibited a brownish or yellow ring around a paler area, in the interior
of which an inner cell was visible, sometimes globular, often irregular
in shape. The examination of the ring was not entirely satisfactory; it
appeared to be sometimes marked with concentric lines having the
appearance of wrinkles. The inner cell had granular contents and a
central nucleus. When perfectly free they were spherical in form, with a
distinct membrane of their own; and colourless, except when acted upon
by reagents. The means employed to determine the existence of these
cells was to soak the spores in muriatic acid; then, upon pressure of
the glass cover, the outer membrane and ringed cells were ruptured, and
the inner cell escaped (Plate III. fig. 46).
Germination may be induced in these spores by keeping them in a moist
atmosphere (fig. 45); but the mode does not differ from that described
above as occurring in the “corn mildew.” Mr. Currey writes:—“I know no
microscopical object of greater beauty than a number of fruits of
_Phragmidium_ in active germination.” By _Phragmidium_ he means the
_Aregma_ of this work, of which _Phragmidium_ is a synonyme.
Well may the reader remark on arriving thus far, “Does all this
examination and detail refer to the fruit borne in the little blackish
spots on bramble leaves, which I have hitherto overlooked?” Ay, and to
several similar spots on other plants. Examine carefully the raspberry
leaves in your garden, and you will probably find similar, but smaller,
pustules also on the under surface (Plate III. fig. 42). We say
_probably_, because none of our British species seem to be equally
uncommon with this. During the past year we examined hundreds of plants,
and did not find a single pustule. This species was named by Dr.
Greville _Aregma gracilis_, which name it still continues to bear (fig.
43). Such a fate will not await you if you should proceed in the autumn
to some chalky district where the burnet is common. Go, for instance, to
Greenhithe or Northfleet, on the North Kent Railway, in August or
September, where the burnet is plentiful, and the leaves will present
the appearance of having been peppered beneath, from the number of
minute pustules of the burnet brand scattered over the under surface
(fig. 30, upper leaflets). Or if you prefer collecting nearer home,
visit some neighbouring garden, if your own does not contain many roses,
and the leaves will be found equally prolific in an allied species (fig.
36). Should gardens and roses be alike unattainable, any bank or wood
will furnish the barren strawberry (_Potentilla fragariastrum_), and
during the latter part of the summer, or in autumn, another species of
_Aregma_ will not be uncommon on the under surface of the leaves (fig.
33). All these species will be found accompanied by the orange spores of
species of _Lecythea_, which some mycologists consider to be distinct
fungi, and others to be merely forms or conditions of _Aregma_. These
spores are represented in Plate III. figs. 31, 34, 37, and 40. From the
magnified figures of the spores of the different species of _Aregma_
(figs. 32, 35, 38, 41, and 43), it will be apparent that they have all
certain features in common, _i.e._, cylindrical spores containing from
three to seven cells. This may be called the _generic_ character, common
to all the species of the genus _Aregma_. Again, each species will be
observed to possess its own distinct features, which may be termed its
_specific_ character. In one, the apex of the spores will be obtuse, in
another acutely pointed, in another bluntly pointed, &c. In one species
the number of cells will usually be four, in another five or six, in
another seven or eight. The stem in one species will be slender and
equal, in another thickened or bulbous. So that in all there will be
some permanent peculiarity for each not shared by the others.
One other form of brand (_Xenodochus carbonarius_), presenting, it is
believed by some, generic differences from all that we have as yet
noticed, remains to be briefly alluded to. This form appears to be very
uncommon in this country, but, when found, is parasitic on the leaves of
the great burnet (_Sanguisorba officinalis_), a plant of local
distribution. The parasite appears to the naked eye in small tufts or
pustules resembling those of an _Aregma_, but, when microscopically
examined, the cells of the spores are found to be numerous, indeed,
considerably more than in the most complex _Aregma_ (fig. 29). This,
however, seems to be the only distinction, for the cells are free in the
interior of the investing membrane, and in all points of structure, in
so far as it has been examined, identical with _Aregma_. Whether it is
logical to consider a four-celled spore an _Aregma_, and a seven-celled
spore an _Aregma_, and exclude a ten or twelve-celled spore from the
same genus on account of the number of its cells, does not appear to us
clearly answerable in the affirmative.
During the course of this and the preceding chapter we have passed
rapidly through four genera of parasitic fungi so nearly allied, that
one is almost led to doubt the validity of the generic distinctions.
These may be presented briefly thus:—
Spores two-celled PUCCINIA.
Spores three-celled TRIPHRAGMIUM.
Spores four to AREGMA.
seven-celled
Spores many-celled XENODOCHUS.
It has been seen that the habit, mode of growth, germination, and
structure, except in the number of cells, scarcely differ; but it is not
our province here to enter upon the discussion of such a subject.
The association of one-celled, orange-coloured spores with the brown two
or more celled spores passed in review is another feature worthy of a
passing notice, and which opens a field for discussion. It is generally
admitted that these two forms are the production of the self-same
mycelium or vegetative system, but it is not so generally admitted that
they are but two forms or phases of the fruit of the same plant. It is
not at all uncommon in the history of mycology to find two forms which
were for a long time considered to be distinct plants producing
different forms of fruit, and which bore different names, and were
located in different genera, at length proved to be only the self-same
plant in different conditions, and ending in one name being expunged
from the list. Such a fate probably awaits, at no distant date, the
orange spores which precede or accompany the species in the present
genera. Already Tulasne and some others accord them no place in their
system.
It may be added, for the benefit of any who wish to pursue the study of
this interesting branch of Cryptogamic Botany, that the leaves of the
plants containing the parasitic fungi now noticed may be collected and
preserved by drying between folds of blotting-paper, or the leaves of a
book, and will retain their character, with the exception of colour in
the orange forms, so as to be eligible for examination at any period of
the year for twenty years to come. Each species, when dry, may be
transferred to an old envelope, and labelled outside with the name, date
of collection, and locality; and one hundred such envelopes will
constitute a miniature herbarium in a very small compass.
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