No species in the entire genus makes so prominent an appearance as the one found on the radical leaves of the spear thistle (Carduus lanceolatus). This latter plant is exceedingly abundant, and so is its parasite (Puccinia syngenesiarum, Lk.). From the month of July till the frosts set in we may be almost certain of finding specimens in any wood. The leaves have a paler roundish spot, from one-twelfth to one-fourth of an inch in diameter, on the upper surface, and a corresponding dark brown raised spot on the under surface, caused by an aggregation of pustules, forming a large compound pustule, often partly covered with the epidermis. The individual pustules are small, but this aggregate mode of growth gives the clusters great prominence, and therefore they are not easily overlooked ([Plate IV.] fig. 63). Although not confined to this species of thistle, we have not yet found this Puccinia on any other plant. The spores are elliptical, rather elongated, constricted, and without spines (fig. 64).
Other species of Puccinia are found on Composite plants, but with none of these is the present fungus likely to be confounded, if regard be had to its peculiar habit. The leaves, for instance, of the common knapweed (Centaurea nigra) are often sprinkled with the small pustules of the centaury brand (Puccinia compositarum, Sch.); these generally occupy the under surface of the lower radical leaves (fig. 67); occasionally a few of the pustules appear on the upper surface. We have not often found this fungus in the neighbourhood of London on the leaves of the knapweed, but, on the other hand, we have encountered it very commonly on those of the saw-wort (Serratula tinctoria). The spores are oval, scarcely constricted, and not attenuated in either direction (fig. 68). Other Composite plants than those above named are liable to attacks from this parasite.
In our school-days we remember to have spent many a stray half-hour digging for “earthnuts,” under which name we, as well as our elders and betters, knew the tubers of Bunium flexuosum. Not then, nor for many years after, did we notice, or regard if we did notice, the distorted radical leaves and leaf-stalks, and the blackish-brown spots, which reveal the cause in the presence of a brand, or parasitic fungus, of this genus (Puccinia Umbelliferarum, DC.), which is extremely common on this, as well as some other allied plants. If any spot is searched where this plant grows in any profusion, before the flowering stalks have made their appearance above the surrounding grass, this Puccinia will be readily found by the twisted, contorted, sickly appearance of the infested leaves (fig. 71), the petioles of which are often swollen and gouty in consequence. The sporidia are shortly stalked, and generally very much constricted (fig. 72). The species found on the stems of the hemlock, and also that on Alexanders (Smyrnium Olusatrum), are distinct; the spores of the latter being covered with tubercles or warts (figs. 55, 56). During a botanical ramble through Darenth Wood in April of the year just passed away, in some parts of which the sanicle abounds, we found the bright glossy leaves of this singular and interesting plant freely sprinkled with the pustules of a Puccinia (P. Saniculæ, Grev.), which is not at all uncommon on this, but has not hitherto been found on any other plant. Dr. Greville, of Edinburgh, was the first to describe this, as well as many other of our indigenous minute Fungi. For many years he has toiled earnestly and vigorously at the lower cryptogams, as evidenced by his “Scottish Cryptogamic Flora,” published in 1823; and yet his continual additions to the records of science show him to be earnest and vigorous still.
We have by no means exhausted the catalogue of Fungi belonging to this genus found in Britain, nor even those commonly to be met with; but the fear of prolixity, and the desire to introduce a description of other forms into the space still remaining to us, prompt us to dismiss these two-celled brands with but a brief allusion to such as we cannot describe. Box-leaves are the habitat of one species, and those of the periwinkle ([Plate VI.] fig. 132) of another. One vegetates freely on the leaves of violets through the months of July and August, and another less frequently on the enchanter’s nightshade. Several species of willow-herb (Epilobium) are attacked by one Puccinia ([Plate IV.] figs. 78, 79), and a single species by another. Plum-tree leaves, bean-leaves, primrose leaves, and the half-dead stems of asparagus, have their separate and distinct species, and others less commonly attack the woodruff, bedstraw ([Plate VIII.] figs. 172, 173), knotgrass, ragwort, and other plants less common, more local, or, to the generality of the non-botanical, but imperfectly known.
We have found, not uncommonly in the autumn, the scattered pustules of a brand on the stems and leaves of the goat’s-beard, occupying the places which were scarred with the remains of cluster-cups that had flourished on the same spots a month or two previously ([Plate IV.] fig. 76). The pustules are by no means minute, but elongated and bullate; the spores beautifully studded with warts ([Plate IV.] fig. 77). This species cannot certainly be identical with Puccinia compositarum (Schlecht), P. syngenesiarum (Lk.), or P. tragopogonis (Corda). In none of these do the spores appear to be warted, and the habits of both the latter are different. Its nearest associate appears to be P. centauriæ (Corda), at least in the fruit, and whilst the form and character of these organs are considered of any value in the determination of species, smooth spores cannot be associated, we think, with tuberculate or echinulate spores under the same name.
In the spores of the species to which attention has been more specially directed we have types of the principal forms. In the “corn-mildew” they are elongated, and tapering towards either end; in the “coronated brand” the apex is crowned with spicular processes; in the “wind-flower brand” the entire spores are echinulate; in the “mint brand” they are globose; in the “composite brand” elliptic; in the “earth-nut brand,” nearly cut in two at the septum; and in the “dandelion brand,” so variable in form that no two are precisely alike. On the other hand, all are characterized by a transverse septum dividing each spore into two cells.
CHAPTER V.
COMPLEX BRANDS.
FROM the twin-spored genus we pass to another, in which the spores are usually divided into three cells, and which, from this cause, has been named Triphragmium. Only one species has hitherto been found in this country, and that not very commonly, on the leaves of the meadow-sweet, Spiræa ulmaria ([Plate III.] fig. 47). Externally, it much resembles, in the size and character of the pustules, many of the above-named brands, but when seen under the microscope this similarity disappears. In general outline the spores are nearly globose, and externally papillose. In one species, found on the Continent, but not hitherto in Great Britain, the spores are covered with curious long-hooked spines, by means of which they adhere tenaciously to each other. In germination, the spores of Triphragmium do not offer any noteworthy deviation from those of Puccinia,[[5]] and the chief interest of our indigenous species lies in the three-celled form of its spores (fig. 48), to which occasionally those of Puccinia variabilis approximate, and may be regarded as the link which unites the two genera.
[5]. Mr. Currey has only seen the tips of the germinating threads swell, and become septate, each of the joints thus formed falling off and germinating without producing spherical sporidia; whilst Tulasne figures globular sporidia, as will be seen in our fig. 49, reduced from the figure by Tulasne.—(Vide Currey, in “Quarterly Journal of Microscopical Science,” 1857, pp. 117, &c.)