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.