Ferns usually produce their little green prothallia above ground, and the perfect plant generally has a creeping rhizome or underground stem. Some, however, have strong, erect, woody stems, such as we see in the tree ferns of tropical and sub-tropical countries. The horsetails and the club-mosses are also produced from prothallia that are formed above ground. The perfect plants of the former have branching underground stems which give off numerous roots, and send up annually green, jointed, aërial stems that bear whorls of fine leaves, each whorl forming a toothed, ring-like sheath. The fertile shoots terminate in cones, on the modified leaves of which the sporangia are produced. The stems of the club-mosses are clothed with small overlapping leaves, in the axes of which the sporangia are produced; and the spores, which are formed in abundance, constitute the lycopodium powder with which druggists often coat their pills. Water ferns either float on the surface of water or creep along the bottom, and produce their fruit either at the bases of the leaves or between the fibres of submerged leaves. The Selaginellas are characterised by a procumbent stem that branches in one plane only, producing small, sessile leaves, with a single central vein. A number of roots grow downward from the under side of the stem, and the fruit is developed in the axils of the leaves that form the terminal cones of the fertile branches. The above are all the principal divisions of the flowerless plants, and we have now to note the general characteristics of the _Phanerogams_. The chief of these is, of course, the possession of flowers as reproductive organs; and although it is not convenient to give a full description of the flower at the present time, it will be necessary to say a little concerning it in order that we may be able to grasp the broad principles of classification.