In 1857, Mr. F. Currey investigated the structure of these spores, and the results of these experiments were detailed in the “Quarterly Journal of Microscopical Science.” One conclusion arrived at was, that “the idea of the fruit consisting of sporidia united together and forming a chain, is certainly not in accordance with the true structure. The sporidia are not united to one another in any way, but, although closely packed for want of space, they are in fact free in the interior of what may be called a sporangium or ascus.” To arrive at this conclusion, careful examination was necessary, and new modes of manipulation essential. The details of one method employed were to the following effect:—A sufficient number of spores were removed on the point of a lancet, and placed on a slide in a drop of alcohol. Before the spirit was quite evaporated, two or three drops of strong nitric acid were added, and the whole covered with thin glass. The slide was then warmed over a spirit-lamp, the acid not being allowed to boil, but only gradually heated to boiling point. By this means the fruit was found to consist of an outer membrane, nearly transparent, and studded with tubercles; that this membrane enclosed a number of cells which constituted the apparent joints, and which were naturally flattened at either end by mutual pressure. When the outer membrane was dissolved or ruptured, these cells escaped, and became detached from each other. The cells, thus set free, exhibited a brownish or yellow ring around a paler area, in the interior of which an inner cell was visible, sometimes globular, often irregular in shape. The examination of the ring was not entirely satisfactory; it appeared to be sometimes marked with concentric lines having the appearance of wrinkles. The inner cell had granular contents and a central nucleus. When perfectly free they were spherical in form, with a distinct membrane of their own; and colourless, except when acted upon by reagents. The means employed to determine the existence of these cells was to soak the spores in muriatic acid; then, upon pressure of the glass cover, the outer membrane and ringed cells were ruptured, and the inner cell escaped (Plate III. fig. 46). Germination may be induced in these spores by keeping them in a moist atmosphere (fig. 45); but the mode does not differ from that described above as occurring in the “corn mildew.” Mr. Currey writes:—“I know no microscopical object of greater beauty than a number of fruits of _Phragmidium_ in active germination.” By _Phragmidium_ he means the _Aregma_ of this work, of which _Phragmidium_ is a synonyme.