ONE of the fungal diseases of corn long and widely known has obtained amongst agriculturists different appellations in different localities. In some it is the “smut,” in others it is respectively “dust-brand,” “bunt-ear,” “black-ball,” and “chimney-sweeper,” all referring, more or less, to the blackish soot-like dust with which the infected and abortive ears are covered. This fungus does not generally excite so much concern amongst farmers as the other affections to which their corn-crops are liable. Perhaps it is not really so extensively injurious, although it entirely destroys every ear of corn upon which it establishes itself. Wheat, barley, oats, rye, and many grasses are subject to its attacks, and farmers have been heard to declare that they like to see a little of it, because its presence proves the general excellence of the whole crop. No one who has passed through a field of standing corn, after its greenness has passed away, but before it is fully ripe, can have failed to notice, here and there, a spare, lean-looking ear, completely blackened with a coating of minute dust (Plate V. fig. 98). If he has been guilty of brushing in amongst the corn, it will still be remembered how his hands and clothing became dusted with this powder; and if at the time he should have been clad in sombre black, evidence will have been afforded—in the rusty-looking tint of the powder when sprinkled upon his black continuations—that, however sooty this powder might appear whilst still adhering to the ears of corn, it has an evident brown tint when in contact with one’s clothes. This powder, minute as it is, every granule of it constitutes a spore or protospore capable of germination, and ultimately, after several intermediate stages, of reproducing a fungus like the parent of which it formed a part. During the growth of the plant its virulent contents flow like a poison through the innermost tissues, and at length attack the peduncle or axis of the spikelets of the ear, raising up the essential organs and reducing them to a rudimentary state. Brongniart, who made this species the special subject of observation, states that the fleshy mass which is occupied by the fungus consists entirely of uniform tissue, presenting large, almost quadrilateral cavities, separated by walls, composed of one or two layers of very small cells filled with a compact homogeneous mass of very minute granules, perfectly spherical and equal, slightly adhering to each other, and at first green, afterwards free or simply conglomerate towards the centre of each mass, and of a pale rufous hue; at length the cellular walls disappear, the globules become completely insulated, and the whole mass is changed into a heap of powder, consisting of very regular globules, perfectly alike, black, and just like the reproductive bodies of other fungi (Plate V. fig. 99). A scientific botanist of some repute, M. Unger, published a work in Vienna during the year 1823, in which he sought to prove that this, and allied species of fungi, were not fungi at all, but merely broken up cells, or disruptured and altered conditions of certain portions of the diseased plants. The most satisfactory refutation of this theory may be found in the fact that the spores of the smut can be seen to germinate under favourable conditions, and produce fruit, whereas, if they were only the ordinary cells of the plant broken up by disease, fructification would not take place.

The spores in this species are exceedingly minute. It has been ascertained that forty-nine of them would be contained within a space the one-hundred-and-sixty-thousandth part of a square inch; hence one square inch of surface would contain little less than eight millions. These myriads of spores are shed from the ears, and nothing remains but the barren matrix in which they were borne when the farmer proceeds to gather in his crops. At that time he sees no more of the “smut,” all remembrance of it for the time is gone, his only thought is to stack his corn in good condition. But the millions of spores are dispersed, ten millions at least for every ear that has been “smutted,”—and will they not many of them reappear next year, and thus year after year, with as much certainty as the grain upon which they are parasitic?

Like many of the parasitic fungi, so destructive in the farm and the garden, this species belongs to the family in which the spores are the distinctive feature. After many botanical changes, the “smut” is at length regarded as a fixed resident in the genus Ustilago; with the specific name of segetum, which latter signifies “standing corn;” it is therefore the Ustilago, or smut of the standing corn. The characters of the genus are, chiefly, that the spores are simple and deeply seated, springing from delicate threads, or in closely-packed cells, ultimately breaking up into a powdery mass. Fifteen members of this genus have been described as British. One of these (U. maydis) attacks the maize or Indian corn grown in this country in a similar manner as the common smut attacks wheat or barley; but as maize is not an established crop with us, a more minute description of this species is unnecessary; the spores are figured in Plate V. fig. 108. Another species (U. hypodytes) makes its appearance at first beneath the sheaths of the leaves surrounding the stems of grasses (fig. 100), and ultimately appears above and around them as a purplish-black dust (fig. 101). The seeds of sedges, the leaves and stems of certain definite species of grass, the flowers of scabious (Plate VI. figs. 123-125), the receptacles of the goatsbeard, the anthers of the bladder campion, and other allied plants, and the seeds of the Bistort family, are all liable, more or less, to the attacks of one or other of the residue of the fifteen species of Ustilago already referred to as indigenous to Britain.

Although we do not profess to teach practical men how to grow good corn, or how they shall get rid of, or keep clear from, the many foes to which their crops are exposed, yet a suggestion may be offered, based upon the facts obtained in our botanical researches, supported by the analogy of allied circumstances. In this instance the extreme minuteness and profusion of the spores would evidently render all the corn liable to the attachment of, perhaps only two or three, spores to the seed coat. Some ears of corn in nearer proximity to the smutted ears may be covered with spores which yet remain invisible to the naked eye, and when these grains are mixed with others in the heap, the chances are not much in favour of any handful not becoming charged with spores. If the majority of these were not redeemed from destruction by the many changes, shiftings, rubbings, and scrubbings to which the seed corn is liable between the time of its reaping and the period of its sowing, we might expect a very large crop of “smutted” corn. Under ordinary circumstances we can scarcely imagine that the loss arising from infected ears would repay much special labour to prevent it, only that to a large extent the precautions taken to cleanse the seed corn from the spores of one fungus will also avail for another, and while cleaning it of the spores of “smut,” those of “bunt” will also be removed. The facts that we rely upon chiefly as indicating the remedy are that the spores are only superficially in contact with the seed corn, and that they are of less specific gravity, causing them to float on the surface of any fluid in which the corn may be immersed. Again, the spores of many species of fungi will not germinate after saturation with certain chemical solutions. One of the most successful and easy of application is a strong solution of Glauber’s salts, in which the seed corn is to be washed, and afterwards, whilst still moist, dusted over with quick-lime. The rationale of this process consists in the setting free of caustic soda by the sulphuric acid of the Glauber’s salt combining with the lime, and converting it into sulphate of lime. The caustic soda is fatal to the germination of the spores of “bunt,” and probably also of “smut;” although, as already intimated, except in cases where these affections of the corn are very prevalent, we shall be informed by the agriculturist that the cost of labour in the prevention will not be compensated in the cure.

Experience has also taught us that many fungi flourish in proportion to the wetness of the season, or dampness of the locality. A wet year is always exceedingly prolific in fungi, and a dry season correspondingly barren, at least in many kinds, whilst others, as the experience of 1864 has convinced us, are exceedingly common. In a field or wood the mycologist reaps his richest harvest of mycological specimens in the lowest and dampest spots, in swamps, ditches, and ill-drained nooks. This is a fact worth knowing as much by the farmer as the amateur botanist in search of specimens for his herbarium.

One of the most unmistakable species of “smut” is that which infests the goatsbeard, on which we have already described an Æcidium. Generally about the same time as the cluster-cups make their appearance on the leaves, some of the unopened flower-heads of this plant will be found considerably altered in appearance by the shortening of the segments of the involucre, and at length by the whole inflorescence being invested with a copious purplish-black dust. If, by any means, the lobes of the involucre are any of them separated, the enclosed dust escapes, blackening the fingers and clothing of the collector, as if it were soot (Plate V. fig. 92). A little of this dust submitted to the microscope will be found to consist of myriads of small globose spores, nearly uniform in size and shape; and if a higher power be employed, each of these will appear to have a papillose or minutely granulated surface. The florets, dwarfed in size and contorted, or the remains of them, are embedded in the mass of spores (fig. 93), and if one or two of these are removed and placed under a good one-inch objective, every part will be found covered with adhering spores, to the apparent exhaustion of its substance. Of course, the florets are never developed when subjected to the attack of “smut.” The whole plant assumes a faded, sickly appearance, even before the spores are fully ripened. We would recommend our readers, if they collect one of the infected flower-heads, to put it into a box or paper by itself, for if placed in the box with other specimens it will so sprinkle them with its black powder as to render them nearly useless for microscopic examination: everywhere the microscope will detect, where the unaided eye failed to recognize a trace, the ubiquitous spores of Ustilago receptaculorum (Plate V. fig. 94).

In the fenny districts of the eastern counties a species of “smut” called Ustilago typhoides attacks the stems of reeds, forming thick swollen patches of several inches in length (fig. 128), sometimes occupying the whole space between two joints or nodes, and lying beneath the sheath of the leaves. The spores in this species are larger than in the species which attacks the culms of grasses in a similar manner (Plate VI. fig. 129).

There are not many features in the rest of the species of this genus of sufficient interest to the general reader or microscopist to render it advisable to furnish any detailed account of them. We may, however, note that in a species found on the leaves of the common cock’s-foot grass the spores are large, obovate, and rough, with minute granules (figs. 117, 118). This species is known botanically as Ustilago salveii, and externally bears considerable resemblance, except in the size and colour of the spores (fig. 119), to another species much more common, and which occurs on the leaves of Poa aquatica and P. fluitans. The last-named species forms long parallel sori, extending often for several inches along the leaves of the aquatic grasses just named, giving them a very singular appearance (Plate V. figs. 105, 106). The spores are small (fig. 107), not being more than one-fourth the length of the last species, and smooth, whilst those are minutely granulated.

An interesting species occurs, very rarely, on the stems of such grasses as Aira cÆspitosa and A. aquatica. The sori are in bands at regular distances apart (Plate VI. fig. 120), each band being composed of a number of short parallel sori (fig. 121). The spores are not more than one-third of the size of those in U. longissima.

Sedges are also subject to attack from other species of smut; one of these (U. olivacea) appears to convert the seeds into a fine olive-coloured dust (Plate VI. fig. 126), which gives to the fruit a similar appearance to that presented by corn when attacked by Ustilago segetum. Another species, which also absorbs the seeds, becomes hardened and consolidated more than in any other species, and, though larger than the normal seeds, still retaining their form (figs. 109, 110). This is Ustilago urceolorum, the spores of which are also figured (fig. 111).

The beaksedge (Rhyncospora alba) suffers from an allied species which affects it in a similar manner (Plate V. figs. 96, 97), but is not equally common. The spores of Ustilago utriculosa, found on different species of Polygonum, instead of being granulated, are reticulated on the surface (Plate VI. figs. 114, 116). The chief interest attaching to Ustilago antherarum consists in its habitat, for it is developed in the anthers of the flowers of the bladder campion, and other plants of the same natural order. The anthers are much swollen and distorted by this parasite, which is not uncommon, though easily overlooked unless specially sought after (Plate V. figs. 102-104). A list of all the British species will be found at the close of this volume. It will be noted that as in the genus Æcidium the prevailing colour of the spores is orange, so in the genus Ustilago it is black, with a purplish or violaceous tinge.

Four diseases in wheat of fungal origin are known and recognized in the popular language of the farm as “mildew,” “rust,” “smut,” and “bunt.” Sometimes one and sometimes another is most prevalent, and he is an exceedingly fortunate individual who can walk through his fields and find only one of them, especially if that one should be sparingly distributed. It has been our good fortune to dwell much amongst cornfields, and the terror of the word “mildew” to a farmer’s ears is not unfamiliar in our reminiscences of the past, ere we discarded the much-loved country to become a dweller in town. The subject of our present remarks inspired no such alarm in the districts of our experience, but in some seasons and localities it is certainly one of the “pests of the farm.” Under the different appellations of “bunt,” “pepper brand,” “bladder brand,” and sometimes “smut,” this infection is very generally known. Externally there is no appearance, except to the practised eye, that anything is wrong. There is no black impalpable dust about the ears as in the true “smut,” no red withered leaves or spotted stem as in the “rust” and “mildew,” and no stunted growth or malformation, evident to the casual glance, by which the insidious foe can be recognized; but stealthily and secretly the work is accomplished, and until the “bunted” grains make their appearance in the sample, the disease may, perchance, be unchallenged.

Externally the “bunted” grain is plumper, and whilst the corn is still green these will be of a brighter green than the rest (Plate V. fig. 84). When broken, the farinaceous interior will be found replaced by a minute black dust of a very foetid, unpleasant odour, and greasy to the touch (fig. 85). This powder constitutes the spores of the “bunt” mixed with myceloid threads. It may happen that much of the corn in a field is “bunted,” and the discovery not made till the wheat is being ground for flour; then the odour and colour will speedily decide the produce to be unfit for human food. We have not the least doubt that “bunted” corn, when ground with flour, is injurious in proportion to its extent, whilst at the same time we can scarcely conceive an intelligent miller grinding up a sample containing any large proportion of “bunted” grains in ignorance of the fact.

If we break open a grain of wheat infested with the “stinking rust” or “bunt,” and then place some of the powder in a drop of water on a glass slide, and submit this to the microscope, first using the half-inch power, then the quarter, or fifth, and finally an eighth or tenth, we shall find that this minute dust consists of myriads of globose brown bodies termed spores, which possess certain reproductive functions. These spores will be found mixed with a number of delicate branched threads, to which they are attached by a short stalk or pedicel, visible with the higher powers (fig. 86). The surface of the spores you will also observe to be beautifully reticulated. These features just described as visible in the “bunt” are the characteristics of the genus to which it belongs (Tilletea), and of which it is the only British species. An allied species infests the Sorghum or durra, a grain but little cultivated in Europe, but found extensively in Africa and Asia, and also apparently found on the Bajra of India.

The interesting experiments of the Rev. M. J. Berkeley on the germination of “bunt” spores have been already alluded to. They were undertaken shortly after the outbreak of the potato disease, to ascertain, if possible, the mode by which the minute spores of fungi inoculate growing plants; and although at that time only a bare suspicion of the nature of the bodies resulting from the germination of “bunt” spores was entertained, succeeding examinations in the same direction have brought to light extraordinary facts, and manifested the progress of the successive developments of four generations. The spores of “bunt” are larger than those of the different species of “smut,” and reticulated on the surface (Plate V. fig. 86). When these are made to germinate a kind of stem is protruded (fig. 87), upon which small clusters of elongated thread-like spores of the second generation, or sporidia, are produced (fig. 88). After a time these spores conjugate, or become united by short transverse processes in the same manner as has been observed in some of the lower forms of AlgÆ (fig. 89). The conjugated spores in the next stage germinate and produce a third kind of fruit, different from either of the preceding, and constituting a third generation (fig. 90). These in turn germinate and produce a fourth order of reproductive organs (fig. 91), so that in the process of growth the “bunt” spores evidently pass through four generations. Hence, as one result, the number of germinating bodies is greatly increased, as well as their power of inflicting injury in a corresponding diminution in size. There are still many points in the history of the growth and development through successive generations of the “bunt” spores, but enough is known, on the one hand, to show that this is a true vegetative parasite, and not merely a diseased condition of the tissues of the wheat plant, and on the other that it is perfectly distinct from all the phases of the other and similar parasitic fungi which affect the wheat crop.