Rust, Smut, Mildew, & Mould: An Introduction to the Study of Microscopic Fungi

by M. C. Cooke

Plate IV.
W. West imp.

A very singular and interesting species is not uncommon on the more delicate grasses, being found chiefly confined to the leaves, and produced in smaller and more rounded, or but slightly elongated, patches ([Plate IV.] fig. 60). We have met with it plentifully amongst the turf laid down in the grounds of the Crystal Palace at Sydenham, and also on hedge-banks and in pastures. The spores are rather smaller than those of Puccinia graminis, but, like them, much elongated, slightly constricted, and borne on persistent peduncles. The most prominent distinction may be found in the apices of the spores, which, in this instance, are not attenuated, but crowned with a series of little spicules, or teeth, whence the specific name of coronata has been derived ([Plate IV.] fig. 62).

The Labiate family of plants and its ally the Scrophulariaceæ are also subject to the attacks of several kinds of Brand, a name, by the bye, often applied locally to the corn mildew and other similar parasites, and which may have originated in the scorched or burnt appearance which the infected parts generally assume. In the former natural order the different kinds of mint, the ground-ivy, the wood-sage, and the betony, and in the latter, the water figwort and several species of veronica, or speedwell, are peculiarly susceptible; and on most a distinct species of Puccinia is found. To provide against doubt which the less botanical of our readers may possess of the meaning or value of the term Puccinia, which has already occurred two or three times in this chapter, a brief explanation may be necessary, which more scientific readers will excuse.

In botany, as in kindred sciences, acknowledged species have their trivial, or specific name, generally derived from the Latin. In the last species referred to, this was coronata, meaning crowned, in reference to the coronated apex of the fruit. Any indefinite number of species with some features in common are associated together in a group, which is termed a genus, and the term prefixed to the specific name of each species constituting that genus is its generic name, also commonly derived from the Latin or Greek. In this instance it is Puccinia, derived from the Greek puka, meaning closely packed, singularly applicable to the manner in which the spores are packed together in the pustules. The common features, or generic distinctions, of this genus, are uniseptate spores borne on a distinct peduncle.

In returning to the species found on Labiate plants, let us suppose ourselves to have strolled towards Hampstead Heath, and south of the road leading from Hampstead to Highgate, near certain conspicuous and well-known arches, built for a purpose not yet attained, are two or three muddy ponds nearly choked up with vegetation. Some fine autumnal afternoon, we must imagine ourselves to have reached the margin of the most northern of these ponds, and amidst a thick growth of reeds, sedges, and other water-loving plants, to have found the water-mint in profusion and luxuriance, with every leaf more or less occupied, on its under surface, with the yellow spores of a species of rust (Trichobasis) mixed with the browner septate spores of the mint brand (Puccinia Menthæ). This is common also on the horse-mint and corn-mint; we have found it on the wild basil and wild thyme, and once only on marjoram. Having collected as many leaves as we desire, and returned to home and the microscope, we proceed to examine them in the same manner as we have already examined the mildew, and as a result of such proceeding arrive at the following conclusions:—The pustules are small and round, never elongated as in the corn mildew, and generally confined to the under surface of the leaves ([Plate IV.] fig. 69). The spores are subglobose, slightly constricted, and the two cells nearly two hemispheres, with their flat surfaces turned towards each other (fig. 70). The form delineated in figure 75 is that of the sorus of many of the epiphytal brands, the centre being occupied by the closely-packed spores, surrounded to a greater or less extent by the remains of the ruptured epidermis.

Although the species of Puccinia (P. glechomatis) found on the leaves of the ground-ivy is said to be very common, we sought it in vain amongst every cluster of that plant met with during last summer and autumn, until, nearly despairing of finding it at all, we at last encountered a plot of ground-ivy covering the ground to the width of two or three yards, and in length eight or ten, nearly every plant being attacked by the brand. This was in the corner of a pasture, and the only time we found infected plants. The fungus, however, may be as common as the plant in other localities. The pustules on the leaves are larger than those of the mints, and also confined to the inferior surface (fig. 73). The spores are elliptic and but slightly constricted; the apex is often pointed, though not always so much as in our figure (fig. 74).

Of other species found on allied plants we have not considered it necessary to give figures, or write much. The betony brand (P. Betonicæ, DC.) does not seem to be common enough to be readily found by any one desiring to examine it for himself; and the same may be said of the figwort brand (P. Scrophulariæ, Lib.), the wood-sage brand (P. Scorodoniæ, Lk.), and the speedwell brand (P. Veronicarum, DC.); all of these are, however, characterized by a distinct feature, or features, which have been considered of sufficient importance to constitute a separate species.

We have had occasion to refer incidentally to the brand found on the under surface of the leaves of the wood-anemone (P. Anemones, P.). This is one of the earliest and commonest species. Go wherever the wood-anemone abounds, in any of the woods lying immediately to the north of the metropolis, or any of the woods in Kent, and from March to May it will not be difficult to find attenuated, sickly-looking leaves, with the under surface covered with the pustules of this brand, looking so like the sori of some fern (fig. 65) that it has been, and still is, sometimes considered as such. In Ray’s “Synopsis” (3rd edition, 1724), it is described in company with the maidenhair and wall-rue ferns; a figure is given of it in the same work (t. iii. fig. 1), and it is stated,—“this capillary was gathered by the Conjuror of Chalgrave.” When, afterwards, it was better understood, and the spots came to be regarded as true parasitic fungi, it still for a long time continued to bear the name, not even yet quite forgotten, of the Conjuror of Chalgrave’s fern.

An examination of the spores, both collectively in the pustules, and separately under a high power, will not fail to convince any one who has examined only the species we have already alluded to, that this parasite on the anemone (P. Anemones) is a true Puccinia, and a most interesting one. The two cells of the spores are nearly spherical, and the constriction is deeper and more positive than in any of the preceding. Moreover, the surface of the spore is minutely and beautifully echinulate, or covered with erect spines ([Plate IV.] fig. 66). Some few other of the species found in Britain have echinulate spores, but those are not common like the present. One word of caution to the amateur in search of the Puccinia on the anemone. It will be fruitless looking for it on the large foliaceous bracts of the flower-stalk, since these may be turned up carefully, till the back aches with stooping, ere a solitary pustule will be found; but the true leaves, proceeding from the rhizomes, are certain soon to afford you specimens.

Everybody knows the dandelion, but it is not every one who has noticed the fungi found upon its leaves. These are most commonly of two kinds, or probably the unilocular and bilocular forms of the same species: the latter we have found in the month of May, and the former in August and September. The lower leaves of young seedlings have generally rewarded us with the best specimens of the septate-fruited brand (Puccinia variabilis, Grev.). The pustules occur on both sides of the leaf, and are very small and scattered (fig. 82). The spores are singularly variable in form: sometimes both divisions are nearly equal in size; sometimes the upper, and sometimes the lower, division is the smallest; occasionally the septum will be absent altogether; and more rarely, the spores will contain three cells. From the very variable character of the spores (fig. 83), the specific name has been derived.