_COMPLEX SMUTS._
SOME of the microscopic fungi are the most unpromising and uninteresting
objects to the naked eye which could well be imagined. No one would
suppose that the black dust so profusely shed in such genera as
_Ustilago_ and _Polycystis_ could be better than as much soot; unless he
has learnt by experience not to judge by appearances, but to suspend
judgment until examination. The axiom will sooner or later force itself
upon all who examine minute objects with the microscope, that all
organic nature, whether animal or vegetable, increases in interest in
proportion to the magnifying power. Seen by the unaided eye, _moulds_
are all nearly alike, and they seem to be “moulds” and nothing more.
“Smuts,” again, sometimes attack one organ, and sometimes another, with
very little variation in colour; and “rusts” are all “only rusts” with a
paler or more intense rusty tint, until the marvellous combination of
lenses, so appropriately named a _microscope_, unfolds a new world, and
exposes its new inhabitants unparalleled in the old world of larger
life, in form, habit, development, and mystery.
A very interesting, though small group of fungi, allied to the
preceding, are included botanically under the genus called _Polycystis_,
in allusion to the many cells of which the spores are composed.[6] In
the most recent work on British Fungi, approximating to a Flora—viz.,
“Berkeley’s Outlines”—only three species are recorded, whilst the most
common, at least around London, is omitted in error; for it could
scarcely have been unknown as indigenous to this country. This last is
the crow-foot smut (_Polycystis pompholygodes_, Lev.), found on the
leaves and petioles of the common creeping buttercup (_Ranunculus
repens_), distorting them very much, and also occurring on the
wood-anemone and some other Ranunculaceous plants. The leaves and their
footstalks, when attacked, become swollen, as if blistered at first, and
ultimately burst in an irregular manner, exposing a mass of blackish
soot-like dust (Plate IX. fig. 183), which on examination will be found
to consist of the many-celled spores alluded to (Plate IX. fig. 184).
Each of these spores appears to have a transparent outer membrane,
either enclosing an unequal number, from two or three to five or six,
distinct cells, compressed together into a spherical form by the outer
integument, or the interior is divided by septa into as many cells. Each
of these divisions contains a dark brownish endochrome, or
cell-contents. As may be anticipated, the spores in all the species
associated in this genus are interesting objects for the microscope. The
species on the buttercup may be found through the summer and autumn on
_Ranunculus repens_, especially whenever that plant is met with in very
damp situations. We have seldom found the plant in any profusion without
its attendant fungus.
Footnote 6:
Rabenhorst has proposed _Urocystis_ as the name of this genus, on the
ground that _Polycystis_ was priorly applied to a genus of Algæ.
Another species of these many-celled smuts is not uncommon in gardens,
on the sweet violet, attacking the footstalks of the leaves more
commonly than the leaves themselves, and swelling and contorting them
(Plate IX. fig. 185). In general structure the spores are very similar
to those of the last species, save that the cells are smaller, and a
larger number are collected together (Plate IX. fig. 186). So far as we
have yet examined the spores of this and the preceding species, they
appear to consist of separate and distinct vesicles (probably spores),
contained within a hyaline sac or outer membrane, and _not_ to be a
single spore divided into cells by numerous septa.
A species of equal interest (_Polycystis Colchici_, Tul.) is found on
the autumnal crocus, or meadow-saffron (_Colchicum autumnale_). The
spores approach nearer to those of the last than of the prior species.
A fourth species occurs on the leaves of rye (Plate IX. fig. 187),
forming elongated parallel blackish lines (_Polycystis parallela_, B. &
Br.). It has also been found on the leaves of some grasses, but does not
appear to be very common.
Many similar features are possessed by the two members of a genus named
_Tubercinia_, which have been found in this country. One of the species
is parasitic upon a plant which we who inhabit southern England never
meet with, but which is not uncommon in Scotland, _i. e._, _Trientalis
Europæa_. The parasite attacks the leaves about the month of September,
forming bullate or blistered patches one-eighth to one-sixth of an inch
broad, containing a mass of black spores (Plate III. fig. 52). These
spores are irregularly globose, large, and opaque, consisting of a
number of distinct cells (Plate III. fig. 53). Never having seen other
than dried specimens—kindly communicated by Dr. Dickie of Aberdeen, the
discoverer of this species—we cannot add much to its history beyond the
published description by the Rev. M. J. Berkeley.
The other species occurs on potatoes, and is, during some seasons,
common in all parts of Great Britain. The spores are curious, being
composed of a number of cells arranged in the form of a hollow sphere,
with one or two apertures communicating with the interior (Plate III.
fig. 54). They are generally attached by a delicate thread. This
species, sometimes confounded with the potato scab, was first described
by Mr. Berkeley, about the time of the appearance of the “potato
disease,” with which, however, it is in no way connected.
Thus it will be seen that, inasmuch as we have complex brands in which
the number of cells are considerably increased, so have we “complex
smuts” in which, instead of one cell, we have many. In the last instance
the two genera associated together in this chapter agree. The spores in
both are distinctly cellular, but in the last genus far more opaque and
consolidated than in the first. Whilst it may be doubted whether the
compound spores of _Polycystis_ are anything more than a number of
individual spores with a gregarious habit, invested with an outer
membrane, such a hypothesis cannot (as far as our individual
examinations extend), be made to include _Tubercinia_. No doubt has yet
been thrown on the genuine character of either of these genera. No
_Uredo_ or _Æcidium_, no _Trichobasis_ or _Puccinia_ has been
ascertained or suspected to appear as a prior or subsequent form. In
their supposed integrity they offer an interesting study, and in their
development a good subject for investigation.
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