Many spores produce the plant directly, others indirectly, as most of the fungi; but if the definition of a perfect plant be that which bears the fructification, the mycelium of a mushroom constitutes the plant, for the mushroom itself is only a kind of sporangium or spore-case. Nevertheless, the spores of the Puccinia and other microscopic fungi, which are the cause of the rust and mildew in wheat, give rise to a kind of prothallus, ‘a slight fore-shadowing’ of the prothallus of the Marchantia and Mosses, which only produce sporangia, and those of the Ferns, Horsetails, and Club Mosses, whose archegonia contain the embryo of the plant itself. The fructification of the Lycopods is the highest of which the Cryptogamia are capable, and brings them into a singular analogy with the flowering class. For in the ovule, or seed-vessel of the flower-bearing race, a large cell is formed, containing mucilaginous matter, which, soon after fructification, is converted into a mass of cellular tissue, which gives rise to the cell containing the embryo, just as the prothallus of a Lycopod gives rise to the archegonium containing the embryo of the plant. The linear leaves of existing Lycopods and the cones of their fossil allies, are similar to the leaves and cones of the Coniferæ: there is no affinity, but an analogy existing between these two groups sufficient to make them form links between the two great divisions of the vegetable kingdom. The Lycopodiaceæ probably may be regarded as the highest of the Cryptogamia, and Coniferæ as the lowest of the flower-bearing class. SECTION XII. GENERAL STRUCTURE OF FLOWERING PLANTS. IN some of the Cryptogamic families fertilization takes place before the plant itself is developed. In the two highest classes, those containing the great groups of Flowering Plants, on the contrary, it is the ultimate result of the inflorescence, which consists of calyx, corolla, stamens, and pistils, all which are the later expansions of the cellular tissues and groups of vessels which have in earlier stages of development formed the leaves. They contain the same materials, and in fact they are leaves modified in form, structure, and function.