CHAPTER IX.
RUSTS.
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).
Plate IX.
W. West imp.
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.