Let us proceed, for the third and last time, to our cornfield, when the corn is nearly or fully ripe, or let us look over any bundle of straw, and we shall find blackish spots, from the size of a pin’s head to an inch in length, mostly on the sheaths of the leaves, often on the culm itself. This is the fully developed _mildew_, and when once seen is not likely afterwards to be confounded with any other parasite on straw (fig. 57). The drawings of Bauer have already been alluded to. Bauer was botanical draughtsman to George III., and his exquisite drawings, both of the germination of wheat and the fungi which infest it, are marvels of artistic skill. A reduced figure from part of one of his drawings is given (Plate IV. fig. 58), exhibiting a tuft of the bilocular spores of _Puccinia graminis_ bursting through a piece of wheat straw. These closely-packed tufts or masses of spores, when examined with a common lens, seem, at first, to resemble the minute sorus of some species of fern; but when seen with higher powers, the apparent resemblance gives place to something very different. The tufts consist of multitudes of stalked bodies, termed spores, which are constricted in the middle and narrowed towards either extremity. The partition, or septum, thrown across the spore at the constriction, separates it into two portions, each of which consists of a cell-wall enclosing an inner vesicle filled with the endochrome (fig. 59) or granular contents, in which a nucleus may often be made out. This species of _Puccinia_ is very common on all the cereals cultivated in this country, and on many of the grasses. A variety found on the reed was at one time considered a distinct species; but the difference does not seem sufficient to warrant a separation. However near some other of the recognized species may seem to approximate in the form of the spores, a very embryo botanist will not fail to observe the distinctive features in the spores of the corn mildew, and speedily recognize them amongst a host of others; subject, as they may be, to slight deviations in form, resulting either from external pressure, checks in development, or other accidental circumstances, or the variations of age.