The whole of this apparatus is called the hymenium. Each of the gills when examined under the microscope is found to consist of a number of elongated cells called basidia, united together on both sides of a cellular stratum, and bearing at their summits four minute spores supported on tiny stalks. It is by these spores, which become detached when ripe, that the plant is propagated. These spores are so very minute that many thousands of them are required to make a body the size of a pin-head; and they are capable of enduring a temperature at least equal to that of boiling water. While upon the subject of spores I may mention here that the remarkable elastic force with which many of the fungi eject their seed has often excited attention, and is fully equal to anything of the same kind observed among flowering plants. The mushroom may be regarded as an ideal fungus of the highest type. There are six large orders of fungi in which the organs of fructification are widely different. The first order is called Hymenomycetes, or naked fungi, because the seed-bearing organs are naked or placed externally. This is the largest, most important, and most highly developed order. The mushroom, toadstool, chantarelle, amadou, are familiar examples of it. The hymenium assumes various shapes in the different genera. In the mushroom it forms gills, in the toadstool tubes, in the chantarelle veins, in the amadou pores, and in the hydnum spines. The second order, called Gasteromycetes, has the seed-bearing organs inclosed in a membraneous covering, like the stomach of an animal, whence the name. The stinkhorn, the Melanogaster, or red truffle of Bath, the bird’s-nest fungus, and the puff-ball are familiar examples of this order. Some of the forms, such as Stemonitis fusca, common on rotten wood, are exceedingly elegant. The third order is called Concomycetes, or dust-fungi, because the spore-cases are produced beneath the epidermis of plants, or the matrix in which they are developed, in the form of a minute collection of dust, entirely destitute of any covering or receptacle, except that which is furnished by the skin of the plant raised around them. This class is the most destructive of the whole tribe. Smut, bunt, and rust are too familiar examples of this most notorious class. The fourth order is called Hyphomycetes, or web-like fungi, because the spores are free, developed or naked filament whose terminal cells are often transformed into a series of spores like a row of beads. The general appearance of the plants belonging to this order is that of a quantity of dust-like seeds, imbedded in a flaky, cottony substance, like a spider’s web. The different kinds of common mould, blue, yellow, and green, the potato disease, caterpillar and silkworm blights, and various kinds of mildew are common examples of this order. The fifth order, called Physomycetes, is distinguished by its stalked sacs containing numerous spores, or sporidea. It is