We have three species of fungi very similar in many respects to the foregoing, but differing in others to such an extent as to justify their association under a different genus and name. The hawthorn is a bush familiar to all who love the “merry month of May,” but it may be that its parasite has been unnoticed by thousands. If, for the future, our readers will bear this subject in their minds when they stand beneath a hawthorn hedge, they may become acquainted with clusters of singular brown pustules on the leaves, petioles, and fruit well worthy of more minute examination (Plate II. fig. 22). They scarcely claim the name of cups, and their lacerated and fringed margins rather resemble the pappus crowning the fruits of some composite plants than the cups of _Æcidium_. The peridia are very long, and split down throughout their length into thread-like filaments of attached cells; these gradually fall away and break up into their component parts till but short portions remain attached to the base of the peridia. These cells are elongated and marked on the surface with waved lines, forming in themselves pretty objects for a high power of the microscope (Plate II. figs. 23, 24). If the teeth of _Æcidium_ resemble the peristome of some mosses, such as _Splachnum_; the threads of this species of _Rœstelia_, except in not being twisted, somewhat resemble the peristomes of other mosses of the genus _Tortula_. The spores in this species are less conspicuous, being of a light brown, and the whole plant, from its modest hue, may be readily passed over without attracting attention unless occurring in abundance. The leaves of pear-trees afford a second species of this genus sufficiently distinct to commend it to our notice. Sometimes it is very common, at others but few examples are to be met with. The clusters occur on the under surface, and consist of half-a-dozen or less of large peridia, pointed at the apex and swelling in the middle so as to become urn-shaped (Plate II. figs. 20, 21). These vessels or thecæ split into numerous threads or laciniæ, which remain united together at the apex. Like the species already noticed, this is brown and inconspicuous except on account of its size, for it is the largest of all that we have had occasion to notice.