Any one may make himself acquainted with the genus _Coleosporium_ with but little trouble, which the acquisition will more than compensate. A summer stroll into any locality in which the common coltsfoot can be found, will be certain to prove sufficient. Let the spot selected be any station on the North Kent Railway, for those who reside in town, or even a trip to the Crystal Palace and a stroll in the grounds, and when the well-known leaves of the coltsfoot are descried, the under surface of the first leaf will doubtless give proof of the presence of the fungus in question, by the orange spores amongst its dense woolly hairs. Sometimes the leaf is almost covered beneath with the bright orange-coloured dust. This is the coltsfoot rust (_Coleosporium tussilaginis_, Lev., Plate VIII. fig. 180), which may serve as a type of the rest. It may be observed that a species of cluster-cup, or _Æcidium_, with spores of nearly the same colour, is also to be found on the leaves of the same plant; but in this case the upper surface of the leaf has also corresponding purplish spots, and, what is of still more importance, the spores are seated in small fringed cups. The rust is common till the wintry frosts have set in, and is far more conspicuous than the cluster-cups. A kind of di-morphism prevails in all the species of this genus. Some of the pustules resolve themselves into a kind of powder, whilst others remain entire and solid. Generally there is the largest proportion of globose, dust-like, free spores, produced in the earliest developed fungi, whilst they become more rare towards the close of the season. The permanent spore-spots consist of obovate cellules placed side by side, each of which is divided transversely by three or four septa, and is filled with an orange-red endochrome (Plate VIII. fig. 181); the exterior being enveloped in a kind of mucous layer. The arrangement of spores when packed together in the pustule is shown in Plate VIII. fig. 182, from an allied species. When these spores germinate, which they do with great readiness, each division emits a long tube, which generally remains simple and undivided, and from its extremity is produced a reproductive body of an obovate or nearly kidney-shape. These filaments are about 1/120th of an inch in length, of a colourless transparent membrane, along which the orange-red contents of the spores pass into the newly-formed sporidia, or reproductive bodies by which they are terminated. Most of these reniform sporidia disengage themselves from the filaments on which they are produced, and either elongate themselves into a simple and uniform filament, or swell at the extremity as if to reproduce a second spore. If the newly-formed sporidia do not become free, they increase the length of their primitive filament, which by a frequent repetition of the process becomes a tube swelling out at unequal distances. [Illustration: Plate X. W. West imp. ]