A QUARTER of a century ago, and all the fungi enumerated in the preceding and in the present and following chapters would have been arranged under three genera, called respectively Æcidium, Puccinia, and Uredo. Under the last-named genus all the species illustrated in the present chapter, beside many others, would have found “a habitation and a name.” There are still a few which bear the old generic name, and, if only out of respect, we shall grant them the first place.

Let the first bright day in May witness the student beside a cluster of plants of Mercurialis perennis, which it will not be difficult to find in many localities, and, on turning up the lower leaves, he will meet with our first illustration of a genuine Uredo, in the form of yellow confluent patches, with a powdery surface (Plate VII. fig. 133). This will be Uredo confluens. By the way, the generic name is in itself suggestive, which it always should be in all instances, but unfortunately is not; it is derived from the Latin word uro, “I burn,” and is peculiarly applicable in instances where the leaves acquire a blistered, burnt, or scorched appearance, occasioned by the presence of the fungus. The microscopical features of the spores of this genus are, briefly, a more or less spherical form, without any pedicel or footstalk Plate VII. fig. 134). These spores are at first produced each in a separate cell, but when ripe become free, and are at times with difficulty distinguished from such forms as Trichobasis, unless the pedicels in the early stage of the latter genus are regarded.

A rare species in Britain is the oak-leaf rust (Uredo Quercus), in which the sori or pustules are minute, and at first yellow, but afterwards orange. It occurs on the under surface of the leaves, and was, we believe, first found in this country by Mr. D. Stock, in the neighbourhood of Bungay, nearly five-and-twenty years since. That gentleman informs us that it was not at all uncommon, but always appeared on the young shoots which had sprung up from the trunks or roots of trees that had been cut down. We are uncertain whether it has been found by any one since that time in this country, although it is not uncommon in France.

The leaves of the common sorrel are often sparely sprinkled with the pustules of a rust (Uredo bifrons, Grev.), which derives its specific name from the fact that the pustules, which appear on both surfaces of the leaves, are often opposite to each other Plate VII. fig. 137). These pustules are generally seated on a discoloured spot (Plate VII. fig. 138 enlarged), and are surrounded by the remains of the ruptured epidermis. The spores are globose and brown Plate VII. fig. 139). We have not met with any other Uredine on the sorrel leaves, though one having a similar appearance to the naked eye is not uncommon on several species of dock.

The fern rust (Uredo Filicum), which occurs on the under surface of the fronds of two or three species of ferns, we have never met with, and do not think that it can be considered common. It has been found in the West of England, on Cystopteris, and Sowerby collected it, probably not very far from London.

One of the most common is the rust found on the leaves of the enchanter’s nightshade (CircÆa lutetiana), sometimes nearly covering the under surface with its tawny snuff-coloured spores Plate VII. fig. 135). The plant on which it is found is rather local, but the rust (Uredo CircÆÆ) seems to abound wherever the plant on which it is parasitic flourishes. Another fungus of a very similar external appearance may be collected, more rarely, from the leaves of the same plant; but in this the spores are two-celled, or divided by a transverse partition. This fact is mentioned to guard against disappointment, should the spores be found to differ from the characters of this section, and to show that the microscope is essential to the study of fungi. The spores of the true Uredo are globose and without any partition Plate VII. fig. 136).

We may also observe that a very interesting species may be found on several species of St. John’s-wort (Hypericum), but especially on the under surface of the leaves of the Tutsan, covering them with its golden-coloured spores (Plate VIII. fig. 174). Another occurs on the leaves of some of the wild garlics (Allium); one is not uncommon on some of the stitchworts; another on saxifrages; another on willow-herbs (Epilobium), and one on the leaves of the cowberry. All of these have yellowish spores. A species with brown spores occurs on sea-lavender (Statice). Space to write on our own part, and patience to read on the part of others, induce us to dismiss all these species with the bare allusion to them and the plants on which they may be found. Some of them may occur in one locality and some in another, and enough has perhaps been said to enable any one to place any that he may find in the proper genus, if not with the scientific name.

From the numerous instances we have met with of persons wholly disinterested in the subject, collecting and making inquiries concerning the bright orange patches next to be referred to, we are led to conclude that most persons have, at least, seen them. These patches of orange-coloured powder burst through the cuticle, and appear on the young branches of wild roses, extending sometimes for two or three inches in length Plate VII. fig. 147), and form one of the most beautiful and obtrusive of the dust-like fungi. It is not confined to roses; but the meadow-sweet, on which it is also found, does not grow in localities where its parasite is so liable to meet the gaze of the ordinary wayfarer. The habit of this rust is more or less that of those which are associated with it. The pustules are not small and orbicular as in most instances in other groups (except Polycystis), but are large and irregular, and generally but few together or single. The spores are variously coloured, and have peduncles, or footstalks, of a greater or less length. In the rose rust these spores are profuse, but the peduncle is short (Plate VII. fig. 148).

Plants of the pea and bean tribe are liable to be attacked by one of these rusts, and in this instance the spores are so characteristic that no one could well confound them with any other. Externally it appears as an irregular brownish pustule, breaking through the epidermis and filled with an impalpable powder, not unlike a pinch of “brown rappee” snuff. The spores are ovoid, with a very long peduncle, whence its name (Uromyces appendiculata). It appears on a great variety of plants, but from the peculiarity of the spores Plate VII. fig. 150), is easily recognized. Our figure represents it on the leaf of a vetch (Plate VII. fig. 149). Almost at the commencement of this volume (Chap. III.) we had occasion to refer in detail to some experiments made by De Bary on the spores of this species. In the remarks then made occurs a recommendation of reperusal, which would obviate any repetition here.

An allied species, and a beautiful one, is to be found on the stinking iris (Iris foetidissima), and another on the under surface of the leaves of primroses.

The pilewort (Ranunculus ficaria) we have already seen attacked by one species of microscopic fungi, and we have now to record the occurrence of another. Some plants appear to be destined both alive and dead to become the prey of others. The common nettle, for instance, as if in retribution for the annoyance it often occasions on account of its stinging propensities, has not less than twenty different species of minute fungi, to say nothing of coleopterous and lepidopterous insects, which make a home, sometimes upon its green leaves, and sometimes on its dead stems. We might almost state that it has a flora and a fauna of its own. The pilewort, too, has many foes; but these are fewer in number, and mostly attack the living plant. The cluster-cups have been already noticed; some do not fall within the limits of this volume, but one, which is found in May and June, belongs to the present genus. It appears like a purplish-brown powder bursting through blistered spots on the leaves and footstalks Plate VII. fig. 156). The spores are small, and are, of course, provided with pedicels Plate VII. fig. 157).

The under surface of the leaves of the white Dutch clover are often sprinkled with black spots, which are nearly round and very numerous. These are so many clusters of fungi belonging to a different section, in which the threads are the important feature. But another parasite is also found on leaves of the same plant, in which the pustules are far less numerous and regular, and are often found on the petiole as well as the leaf, distorting them and twisting them in various directions Plate VII. fig. 154). This is the clover rust (Uromyces apiculata, Lev.), which is a parasite on numerous plants, being found also on the great water-dock and other kinds of dock. The spores are ovoid and brown, with a short peduncle (Plate VII. fig. 155). A very beautiful species occurs on the leaves of the ladies-mantle (Alchemilla), but hitherto we have not been fortunate enough to collect it.

It can scarcely be too great an assumption to suppose that every one is acquainted with the goat-willow (Salix caprea), or that every schoolboy knows the birch (Betula alba). It may be proceeding a step too far to affirm that all who know these trees well enough to distinguish the one from the other, will have observed the under surfaces of the leaves of both sprinkled with a golden dust, during the summer months, and which are the spores of a parasitic fungus. So common is this orange-coloured powder on leaves of the trees above-named, that we can hardly believe any one to have had a branch of either in his hand and not observed it, provided any leaves adorned the branch in question. What this parasite is, and what its associates, it is our province to endeavour to explain. Our figure (Plate VIII. fig. 160) represents a leaf of the sallow or goat-willow, with the under surface exhibiting yellow patches, consisting of spores, which are magnified in the next figure (Plate VIII. fig. 161). This exceedingly common rust is termed Lecythea caprearum, Lev., when in the condition figured; but in reality this is only the summer stage, bearing the summer fruit of Melampsora salicina, which latter attains its mature development on the same leaves in the succeeding winter (Plate IX. fig. 191) or early spring. Of course this latter remark applies to the fallen leaves, for at this period all the willows and other deciduous trees are bare. But the leaves, before they fall, give evidence of the parasite at work; and if the collected decaying mass of rubbish at the base of sallow bushes be examined about March, these leaves will be found bearing upon them mature heaps of elongated, wedge-shaped spores, closely packed side by side (Plate IX. fig. 192), and which, whilst still adherent, may often be found in active germination, as represented in an allied species at the bottom of our plate (Plate IX. fig. 197). This phenomenon consists in the production of cylindrical tubes, more or less elongated, from the upper extremity (rarely from the base) of the prismatic spores. These tubes are straight or twisted, simple or forked, and each of them becomes divided by transverse septa into four unequal cells towards their apex, from each of which is produced a spicule bearing a sporidium, or spherical secondary fruit, in the same manner as in the genera Puccinia and Aregma. It should be observed, that the winter spores of this rust are borne on the opposite surface of the leaves to the summer spores: for whilst the latter are developed from the under surface, the former are found on the upper. This being also an instance of di-morphism, the summer condition, when spherical spores are produced, should not be regarded as a distinct plant, and the name of Lecythea caprearum does not merit retention in the list of fungi.

There are five species of this interesting group, or genus, found in Great Britain, to the residue of which we may only briefly allude. It has already been stated that, in summer, the yellow spores of a rust are found on the under surface of birch-leaves. These must be sought on the young twigs or suckers, proceeding from the stumps of trees which have been cut down: pale discoloured spots on the upper surface of the leaves indicate the presence of the rust beneath. This is the Uredo betulina of old authors (begging their pardons, for some of them still live), the Lecythea longicapsula of more recent times, and the summer spores of Melampsora betulina, according to M. Tulasne and his disciples. When fresh, it is reputed to exhale a faint odour, as of the primrose. During the winter and spring months the wedge-like spores of the second crop are matured on the fallen leaves (Plate IX. figs. 189, 190), and these are capable of a speedy germination, and the production of secondary reproductive bodies, as in the willow rust above alluded to.

Probably, also, the similar rust on the poplar (Plate IX. figs. 195, 196), or on the aspen, may be met with under like conditions; i.e., the summer spores, which are yellow and spherical, on the living leaves, and the brown permanent masses of winter spores on the fallen and decaying leaves. The sole remaining British species is not uncommon on leaves of the common spurge in gardens, and whilst the yellow pulverulent spores occur on the upper, it will not be improbable that black permanent spots will be found on the lower leaves (Plate IX. figs. 193, 194), enclosing closely-packed, rudimentary, elongated or wedge-shaped cellules of the winter spores.

Any one may make himself acquainted with the genus Coleosporium with but little trouble, which the acquisition will more than compensate. A summer stroll into any locality in which the common coltsfoot can be found, will be certain to prove sufficient. Let the spot selected be any station on the North Kent Railway, for those who reside in town, or even a trip to the Crystal Palace and a stroll in the grounds, and when the well-known leaves of the coltsfoot are descried, the under surface of the first leaf will doubtless give proof of the presence of the fungus in question, by the orange spores amongst its dense woolly hairs. Sometimes the leaf is almost covered beneath with the bright orange-coloured dust. This is the coltsfoot rust (Coleosporium tussilaginis, Lev., Plate VIII. fig. 180), which may serve as a type of the rest. It may be observed that a species of cluster-cup, or Æcidium, with spores of nearly the same colour, is also to be found on the leaves of the same plant; but in this case the upper surface of the leaf has also corresponding purplish spots, and, what is of still more importance, the spores are seated in small fringed cups. The rust is common till the wintry frosts have set in, and is far more conspicuous than the cluster-cups. A kind of di-morphism prevails in all the species of this genus. Some of the pustules resolve themselves into a kind of powder, whilst others remain entire and solid. Generally there is the largest proportion of globose, dust-like, free spores, produced in the earliest developed fungi, whilst they become more rare towards the close of the season. The permanent spore-spots consist of obovate cellules placed side by side, each of which is divided transversely by three or four septa, and is filled with an orange-red endochrome (Plate VIII. fig. 181); the exterior being enveloped in a kind of mucous layer. The arrangement of spores when packed together in the pustule is shown in Plate VIII. fig. 182, from an allied species. When these spores germinate, which they do with great readiness, each division emits a long tube, which generally remains simple and undivided, and from its extremity is produced a reproductive body of an obovate or nearly kidney-shape. These filaments are about 1/120th of an inch in length, of a colourless transparent membrane, along which the orange-red contents of the spores pass into the newly-formed sporidia, or reproductive bodies by which they are terminated. Most of these reniform sporidia disengage themselves from the filaments on which they are produced, and either elongate themselves into a simple and uniform filament, or swell at the extremity as if to reproduce a second spore. If the newly-formed sporidia do not become free, they increase the length of their primitive filament, which by a frequent repetition of the process becomes a tube swelling out at unequal distances.

The summer spores, or pulverulent spores of the first generation, which are analogous to the Uredospores of Aregma, are also capable of germination, for, if placed in favourable circumstances, they will develop very long filiform processes, which either remain simple or become more or less branched, but always nearly uniform in their diameter. M. Tulasne states that he has observed this germination many times, though we have been less fortunate.

Of the six species of this genus known to occur in Great Britain, the majority may be commonly met with. That very widely-diffused plant, the wood cow-wheat (Melampyrum pratense), known well to all amateur botanists for its pertinacity in drying black, and presenting anything but an inviting appearance to claim for it a place in the herbarium—also becomes the matrix for the development of a member of this genus; i.e., the cow-wheat rust (Coleosporium Rhinanthacearum, Lev.), and which is found on other allied plants, as the little eyebright (Euphrasia officinalis), &c. (Plate VIII. fig. 176). In colour and habit it resembles the last-named species, and its free, echinulate spores (Plate VIII. fig. 177) form a pretty object for the microscope.

Another equally common species is found inhabiting the leaves of the sow-thistles (Sonchus arvensis and S. oleraceus), and in the autumn may generally be found on either of those plants, presenting the appearance delineated in our plate (Plate VIII. fig. 178). The permanent spores resemble in many points those of the first species, as will be seen from the figure from De Bary’s treatise on this subject (Plate VIII. fig. 179). This is certainly one of the most showy of uredinous fungi, and could not be well overlooked.

The butter-bur rust (Coleosporium petasites, Lev.) and the Campanula rust (Coleosporium CampanulÆ, Lev.) are found, the former on the leaves of the butter-bur, and the latter on those of the harebell and other CampanulÆ, less frequently. We have, however, indicated sufficient, since their great similarity in unprofessional eyes will furnish, in one or two species, all that is desirable for the microscopist.

Unless some similar plan to the following be adopted for examining the species of this genus, it may result in disappointment; for the slight attachment of the joints to each other will otherwise present only a mass of simple echinulate cellules, if a portion be only removed from the leaf on the point of a lancet. This method consists in making a thin vertical section of a pustule in which the spores are contained; by this means the arrangement of the fruit and the mucedinous threads from whence they proceed may be observed. Any person possessed of the cardinal virtues of microscopy—patience and perseverance—will be rewarded in this instance; whilst those who are deficient will lose an object worthy of the virtues they dare not boast. But few instances have occurred in this and the preceding chapters in which the exercise of any great ingenuity or application has been called for; the most juvenile or truest tyro at the microscope may see for himself much of what has been indicated, whilst a few opportunities have occurred for more practised manipulists to prove that they are neither juveniles nor tyros.