UNFORTUNATELY, this group of fungi contains species but too well known for their ravages amongst graminaceous plants, especially the cereals. “Corn rust,” as it is generally called, has a reputation little better than mildew, and it really deserves no better, for it is only another form of that pest of the farm, from the mycelium of which the corn-mildew is at length developed. There are two species very closely allied (doubtless only forms of the same species with different spores) which attack the leaves and culms of growing corn, and, bursting through the cuticle in the manner represented in Plate VII. fig. 141 (magnified), give a peculiar rusty appearance to the plant, as represented in Plate VII. fig. 140. One of these corn-rusts is botanically named Trichobasis rubigo-vera (Lev.), or the “true rust Trichobasis;” the latter, which is the generic name, being a compound of two Greek words (thrix, a hair, and basis, a foundation), on account of the spores being at first furnished at their base with a short, thread-like peduncle, which at length falls away (Plate VII. fig. 142). The other Corn rust is Trichobasis linearis, or “line-like Trichobasis,” because the sori or pustules are linear, or lengthened out like a line; the spores nearly double the length of those of the other Corn rust (Plate VII. fig. 144), and not so bright in colour. By intermediate forms these two rusts pass insensibly the one into the other, so that it is sometimes difficult to distinguish them. Both have the spores clustered together in the pustules, at first (Plate VII. fig. 143) attached by their peduncles, but they soon become free, and are scattered like rust-powder over the plant. Adverting to the attack of rust upon the wheat crops to an unusual extent a few years since, the Rev. M. J. Berkeley wrote as follows:—

We have seen rust more prevalent in white wheats, especially in the variety called Russian white, which has red smooth chaff, than we ever remember it. It is, however, confined to particular spots; and while in one field not a single leaf is free, insomuch that a person walking through the wheat is completely painted with the spores, of a fine rust-red; an adjoining field, separated only by a hedge, has not a rusty leaf. So long, however, as the rust is confined to the leaf, it is, we believe, perfectly harmless. The grain swells in spite of it, and the only effect is that the flag dies a little earlier, which is not undesirable when it is too luxuriant. If, however, it gets to any extent upon the chaff, much more if it attacks the seed itself, as is sometimes the case, it is very mischievous.

There is, indeed, a notion that rust is merely a form of mildew, and this may be true; but if so, it is a harmless form. The true rust (T. rubigo-vera), if a form of mildew, preserves its own characters to the end, and merely presents a second form of fruit, a circumstance which is exceedingly common amongst the lower fungi. It may exist in company with the mildew, but it also more frequently is developed without a trace of mildew intermixed. As far, then, as its immediate effects upon the plant go, it may be treated as a distinct parasite, though advanced botanists may look upon it as offering a case of what they call dualism, which may be easily understood on a comparison with such plants as marigold and orache, which produce seeds of two different forms. Its ultimate effects may, indeed, be injurious, as, if it be really a second form of mildew, it is capable of propagating that pest. The case is quite different with Trichobasis linearis, which is in fact merely the young state of the mildew. When once that supposed species makes its appearance, it is quite certain that there will be mildew to a greater or less extent. While the spores of the one remain unaltered, though intermixed with the true bipartite spores of the mildew, the other exhibits every intermediate state of form and colour.

M. Tulasne, to whom we have already alluded as a high authority on this subject, is of opinion that all the species enumerated in this group or genus, are mere conditions of other species, and therefore excludes it altogether. Another genus (Lecythea), for the same reason, has shared the same fate.

It must not be forgotten that twenty-eight species of rust belonging to this genus are now recorded as occurring in Great Britain. Some of these have yellow or yellowish spores; the rest have the spores of a decidedly brown colour. One of the most attractive of the yellow-spored species is that which appears on the groundsel (T. Senecionis), and a good notion of its external appearance may be gained from our figure (Plate VII. fig. 145). It is not always to be found without searching closely, for in some localities we have found it very sparingly, whilst elsewhere—as, for instance, on Wandsworth Common—we have met with it as soon or as late as there were groundsel leaves for it to grow upon. No spot or change in the appearance of the upper surface of the leaves indicates the presence of the parasite beneath; this is, however, often betrayed by the golden-yellow streaks which appear on the stem. Many a time and oft the boys in the semi-rural districts about town have marvelled and questioned each other concerning the reason why, in gathering “groundsel” for the little bird at home, we should be so particular, and pass so many promising plants, plucking here and there a leaf, and seldom collecting one which they consider eligible for the purpose. Collectors of minute fungi must expect to overhear occasionally even hints touching their sanity from those who, without the remotest idea of their mission, think they must be slightly “wrong in the head” to gaze so narrowly and intently, amongst nettles, groundsel, grass, or dry leaves, and only take an occasional fragment of a rotten stick, or two or three sickly leaves, carefully deposit them in their wallet, hat, or pocket, and then “move on.”

It will be unnecessary to repeat what has been stated in a former chapter on spermogones. It will be remembered that these organs are found developed in connection with some of the species of the present genus, as well as with the cluster-cups, or Æcidiacei. They consist externally of small conical elevations, pierced at the apex, which contain minute, cellular, linear bodies called spermatia, invested with a kind of mucous substance, that over-flows with them from the orifice of the spermogone, like lava from the crater of a miniature volcano. The rust in company with which they have been found most plentifully, is that which covers the under surface of the leaves of the commonest of all thistles (Cnicus arvensis). The external form of one of these spermogones is figured Plate VII. fig. 153. The rust possesses, when fresh, a peculiar odour, which is said to resemble that of orange-flowers; whence was derived its name of “sweet-smelling rust” (Trichobasis suaveolens, Lev.). M. Tulasne writes:—“With respect to this species, it is, in my opinion, but the first form of a Puccinia, analogous to P. Compositarum, D.C.: the spermogones with which it is mixed being very abundant, it ought to be placed with that Puccinia. I should, perhaps, retain some doubts upon the legitimacy of this relationship, if it had not been my fortune to meet on another species of the same kind (Puccinia Anemones, P.) spermogones perfectly characterized, and in which the colour, habit, and position would not allow me to hesitate an instant in attributing them to the Puccinia.” In this species of rust the whole under surface of the leaf is covered with a purplish-brown dusty coating of the spores, from the numerous pustules which are produced (Plate VII. fig. 151). The plants, when attacked, have a paler and more sickly appearance; the leaves have a tendency to fold backwards at their margins, and thenceforth their growth seems to be determined. Sowerby, in his “British Fungi,” says:—“Two or three sorts of flies are occasionally found dead on this plant at the time of the fungus being upon it, which is after wet weather in the summer, or early in autumn; being apparently tempted by its flavour, they over-eat themselves, or else are destroyed by some poison.” This rust has spores resembling, in general characters, those of the yellow-spored series Plate VII. fig. 152).

We have not thought it necessary to give figures of many species, partly on account of the uncertainty existing in many minds whether they ought to be regarded as species, and whether they will long claim a place in the British Flora; and partly on account of the similarity which exists between them, at least so far as they are of interest to the microscopist only.

During the autumn of last year, whilst on a botanical excursion through a portion of Epping Forest, the “great bog” became a centre of some interest. Bogs are generally attractive spots to those who are in search of microscopic organisms. On this occasion the chief objects of interest were the small brown pustules (Plate VIII. fig. 168) with which the upper surface of a large number of the leaves of the pennywort (Hydrocotyle vulgaris) were sprinkled. These pustules were brown, orbicular, regular, and in habit seemed to resemble rather those of most of the PucciniÆ than of a Trichobasis. The large, vigorous, and healthy leaves were less affected. Microscopical examination, at first incomplete, led us to the conclusion that it was a species of Uredo, which had been met with in France (Uredo Hydrocotyles, Mont.); but a re-examination, to which we were prompted by Mr. Currey, led to the conclusion that it belonged rather to the present genus; but it can scarcely be associated with any species already described, notwithstanding its apparent affinity with the brown rust found on umbelliferous plants, in which the pustules are invariably developed on the under surface. Under these circumstances, we have called it the Pennywort rust (Trichobasis Hydrocotyles), whilst still doubtful whether it is not the same fungus as that described by Montagne, with whose description it agrees in everything, except what is implied by the generic name. It should not be forgotten, that the work in which Montagne first described this species was published when the genus Uredo embraced the present genus, which was separated from it by Leveille twelve years later; and it is possible that this species was included in a more recent work by the same author, in error and without re-examination, under the old name. An examination of authentic specimens of Montagne’s plant would settle the point; but we know of no published collection which contains it. The characteristic difference between the two genera lies in the presence of a peduncle in the early stage of Trichobasis Plate VIII. fig. 169), and its absence in all stages of Uredo. Without wandering further into a subject which has not the merit of being very popular, let us away to some green lane in search of violets, and having found them, take a little of the brown dust from one of the small pustules on the leaves, upon the point of a penknife; place this, with a drop of water, upon a glass slide, and make a record of what we observe.

The field is covered with the myriad spores of a rust of a nearly spherical shape, brownish in colour, and here and there one with a short transparent colourless stalk or pedicel. This is the violet rust (Trichobasis Violarum, B.), very common all through the summer and autumn, generally on the under surface of the leaves of violets, in woods and hedgerows. Should it so happen that the spores when placed under the microscope are found to be two-celled, it will prove that instead of a rust, or Trichobasis, being under examination, a brand, or Puccinia, has been found, which is almost equally common, and which may, without such a test, be easily mistaken for a rust. According to the theory of di-morphism, this is the higher form or complete fruit of the same fungus, which in its simple-celled state is called Trichobasis Violarum.

A similar circumstance may befall the student in examining the rust of labiate plants (Trichobasis Labiatarum, Lev.), which occurs on different species of mint, especially the water-mint, about the month of August. We have found a few of the two-celled spores of the Puccinia imbedded in the pustules of this rust almost constantly, whilst the one-celled spores are not uncommon in the pustules of what is regarded as the true mint brand (Puccinia MenthÆ, P.).

In spring the young leaves of the periwinkle (Vinca major) will, in some situations, become thickened considerably, and ultimately browned on both faces with the pustules of a rust (Trichobasis VincÆ), which though covered with a conidioid dust are often very tardy in bursting the epidermis. It is almost impossible, after the pustule is ruptured, to find one in which the bilocular spores of Puccinia (fig. 132) are not largely intermingled with the unilocular spores of the “rust” (Plate VI. fig. 131). Later in the season by two or three months, other leaves of the same plants will be found occupied by the smaller and more widely scattered pustules of Puccinia VincÆ, in which the unilocular spores of the “rust” will seldom be found. In this instance the leaves are scarcely thickened, and the colour of the spores is much darker. The under surface of the leaves is commonly alone occupied, and corresponding paler spots on the upper surface indicate the presence of the parasite beneath.

The garden and field bean is liable in some seasons to become quite rust-coloured in consequence of the profusion of spores with which the leaves and stems are covered, from the bean rust (Trichobasis FabÆ, Lev.), which in like manner is considered as the simple stage or form of the bean brand (Puccinia FabÆ, Lk.). If the legumes are also examined, a few pustules will sometimes be found on them. Beans thoroughly infected with this rust or brand are seldom of much service in either field or garden.

Beetroot, or mangold wurzel, is another example of garden and field produce which is subject to a similar visitation. This rust often has very red spores when produced on red varieties of beet. During September, 1863, it (Trichobasis BetÆ, Lev.) was sent us on the leaves of the wild beet (Beta maritima).

All the species of Polygonum are exceedingly subject to the attacks of the Persicaria rust (Trichobasis Polygonorum, B.), which nearly covers the leaves, till the entire plants seem to be smothered in Scotch snuff. If it were allowable to affirm of any plants that they are martyrs to parasitism, such might be said of the Persicarias and their allies.

Sedges are subject to the attacks of a rust much resembling the corn rust. When it occurs on some species of Carex, the upper surface of the leaf has corresponding pale spots, and the pustules themselves are surrounded by a yellowish margin. This species (Trichobasis caricina) is far from uncommon (Plate VIII. figs. 170, 171). The sedge-like plants belonging to the genus Luzula have also their own species of rust (Trichobasis oblongata), the spores of which are deeper in colour than in the sedge rust (Plate VII. figs. 158, 159).

Amongst the remaining species of Trichobasis (the reader must pardon our using the generic name, as we have no equivalent), that found on the leaves of various composite plants is the most common (Trichobasis Cichoracearum, Lev.). It occurs on some thistles, on the saw-wort, dandelion, several species of hawkweed, and similar plants. The pustules are small and more diffused than in the species found on Cnicus arvensis, and they as often appear on the upper as on the lower surfaces of the leaves.

On umbelliferous plants three species are recorded; one with yellow spores (Trichobasis Petroselini, B.); another with a blistered habit, and brown, ovate, or oblong spores (T. Umbellatarum, Lev.); and a third with tawny, obovate, or egg-shaped spores (T. Heraclei, B.), which is found solely on the cow-parsnip. The species of Puccinia corresponding to some of these species of Trichobasis are known, but, in other cases, probability, or speculation if you please, occupies the place of knowledge.

During the month of September, 1864, it was our good fortune to spend a week in revisiting the scenes of our boyhood, and exploring the minute botany of one of the marshy districts of East Norfolk. One day of the seven, memorable to us for the discovery of three specimens of a large Boletus (B. cyanescens),^[7] not found, to our knowledge, since the days of Sibthorpe, was further enriched by a species of Trichobasis, new to Britain, and apparently uncommon on the Continent. This rust was found on the leaves of the “grass of Parnassus” (Parnassia palustris) on a narrow strip of marsh near Irstead church. It was sought in vain elsewhere. The leaves were scarcely changed in appearance, except by the presence of the pustules. There were no discoloured spots, but the pustules appeared sometimes plentifully, more often scattered, on both surfaces of the leaves: they were small, of a bright brown, with oval spores; the latter were, in their early stages, shortly stalked. We have called this species Trichobasis ParnassiÆ. It is possibly the same as published by Westendorp in his “Herbier Cryptogamique Belge” as Uredo ParnassiÆ, but we know of no copy which we can consult, and have failed in discovering any other species to which we can refer it. It is certainly a Trichobasis and not an Uredo, according to the present limitation of the latter genus.

Although the evidence against the retention of the species of Lecythea (as the genus is named) amongst Fungi as true species, on the ground of di-morphism, is even stronger than against the group just illustrated, we cannot pass them altogether in silence, especially in a popular treatise. Those who are residents in town, and yet possess their little plot of garden-ground, with only two or three pet roses, may have had the misfortune of seeing them smothered with a yellow blight. This golden visitation, unwelcome as it is, may afford a subject for the microscope, and for a small space in this chapter. At first there will not appear to be any important difference between the spores of the yellow series of the last genus and those of the present; but a closer examination will reveal one important distinction, viz., the presence of colourless elongated, abortive spores. The species are not so numerous by half as those of Trichobasis, even when three anomalous forms are included, which species are included by some mycologists in two other genera. One very common rust of this group has already been alluded to (Plate II. fig. 37), and which is known botanically as Lecythea RosÆ. A similar one is found on the bramble, and another on the burnet. All these three species are produced at first on spots which are afterwards more or less occupied by the long, many-celled spores of the dark brown brands called Aregma or Phragmidium, between which and the simple yellow spores of the rust almost every intermediate form may often be found in the same pustule. Thus, from the same mycelium as that of the rose rust, the rose brand is afterwards developed; whilst from the nidus of the bramble rust (Plate III. fig. 40) the bramble brand is also at length produced; and the successor to the burnet rust (Plate III. fig. 31) is the burnet brand. Besides these, a rust belonging to the same genus may be found on the leaves of the poplar, the spurge, and the common valerian, and two or three species on willows. It can scarcely have escaped notice, that the goat-willow is almost constantly afflicted with a rust on the under surface of the leaves (Plate VIII. fig. 160). This species will again come under notice as the summer spores of a truly dimorphous species.

One of the rusts separated by some botanists from this genus is found (possibly most commonly) on the leaves of the raspberry; but during the past autumn we have met with it plentifully on the upper surface of the leaves of one or two species of bramble, and have never seen it growing on the raspberry, although in all descriptions of the species that is stated to be its habitat. Even to the naked eye this is so distinct, that no one could well confound it with any other. It appears very late in the autumn, and the spots are scattered at some distance apart from each other (Plate VIII. fig. 162); each spot or pustule forming a ring (Plate VIII. fig. 163 enlarged) encircling a cluster of spermogones which occupy the centre.

Another rejected species (Lecythea Lini, Lev.) occurs on the little purging flax (Linum catharticum), forming small pustules on the leaves (Plate VIII. fig. 165); these burst irregularly, and remain surrounded by the remains of the ruptured epidermis (Plate VIII. fig. 166). The yellowish spores are subglobose (Plate VIII. fig. 167), and in the first instance concatenate, or chained together like a necklace, which circumstance has been taken advantage of to place it, with one or two other species, in a separate genus.

We cannot claim for the species brought into notice in the present chapter any attractive features resulting from singularity of form, complexity of structure, or delicate tracery, whereby they might commend themselves to mere “searchers after curiosities,” or be recommended from friend to friend as “sensation” objects for the microscope. They do possess an interest and a value, but such as would not be appreciated by those who seek to pass an idle half-hour by gazing at some new thing.