The vegetable kingdom is divided into sections, according to the simplicity or complexity of structure. Associated with plants of simple structure we find, as a rule, more elementary organs of reproduction. Linnaeus made two great divisions, of flowering (_Phanerogams_) and flowerless plants (_Cryptogams_).... The higher group have flowers, with their stamens and pistils, which produce seeds, while the lower group are without flowers and bear spores, which are much simpler bodies than seeds. There are seven main groups of spore-bearers--the _algæ_ or water-weeds; the _fungi_ or mushroom family; the _lichens_, which cover old walls and rocks with patches of coloured vegetation; the _mosses_ with their green leaves and urn-shaped fruit; the _ferns_ with their large and usually much-divided leaves, on the back or edges of which the spores are borne; the _horsetails_, found in wet places, having jointed hollow stems and spores produced in little cones; and the _club-mosses_, upright or creeping leafy plants found on our mountains. These seven groups may be arranged in two divisions, according to the tissues of which they are formed. In the first four the whole plant is composed of _cells_, while in the last three a firm _vascular skeleton_ is present. These characters are of great importance to the student of fossil plants.... The flowering plants are more complex in their structure, and in their organs of reproduction. The lowest group of these plants is the _Gymnosperms_, or naked-seeded plants, like our yews and pines. The other flowering plants (_Angiosperms_) have their seeds in a closed fruit. These are divided into two sections from characters derived from the embryo plant in the seed, depending on whether this minute plant has one seed-leaf (_cotyledon_) or two, and so we have _Monocotyledons_ and _Dicotyledons_. The higher group, or dicotyledons, have been arranged into three divisions, according to the complexity of the flower. In one large group (_Apetalae_) the pistil and stamens are not surrounded by petals, e.g. in the oak and the stinging nettle: superior to them are the plants (_Monopetalae_) in which the petals form a cup, as the blue-bell[249] and the gentian, while the highest group (_Polypetalae_) have all the petals separate, as the buttercups and roses.[250]