CHAPTER VII.
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.
[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.