During the autumn of last year, whilst on a botanical excursion through a portion of Epping Forest, the “great bog” became a centre of some interest. Bogs are generally attractive spots to those who are in search of microscopic organisms. On this occasion the chief objects of interest were the small brown pustules (Plate VIII. fig. 168) with which the upper surface of a large number of the leaves of the pennywort (_Hydrocotyle vulgaris_) were sprinkled. These pustules were brown, orbicular, regular, and in habit seemed to resemble rather those of most of the _Pucciniæ_ than of a _Trichobasis_. The large, vigorous, and healthy leaves were less affected. Microscopical examination, at first incomplete, led us to the conclusion that it was a species of _Uredo_, which had been met with in France (_Uredo Hydrocotyles_, Mont.); but a re-examination, to which we were prompted by Mr. Currey, led to the conclusion that it belonged rather to the present genus; but it can scarcely be associated with any species already described, notwithstanding its apparent affinity with the brown rust found on umbelliferous plants, in which the pustules are invariably developed on the _under_ surface. Under these circumstances, we have called it the Pennywort rust (_Trichobasis Hydrocotyles_), whilst still doubtful whether it is not the same fungus as that described by Montagne, with whose description it agrees in everything, except what is implied by the generic name. It should not be forgotten, that the work in which Montagne first described this species was published when the genus _Uredo_ embraced the present genus, which was separated from it by Leveille twelve years later; and it is possible that this species was included in a more recent work by the same author, in error and without re-examination, under the old name. An examination of authentic specimens of Montagne’s plant would settle the point; but we know of no published collection which contains it. The characteristic difference between the two genera lies in the presence of a peduncle in the early stage of _Trichobasis_ Plate VIII. fig. 169), and its absence in all stages of _Uredo_. Without wandering further into a subject which has not the merit of being very popular, let us away to some green lane in search of violets, and having found them, take a little of the brown dust from one of the small pustules on the leaves, upon the point of a penknife; place this, with a drop of water, upon a glass slide, and make a record of what we observe.