Division III.--=Pteridophyta or Vascular Cryptogams=, =Fern-like Plants= having leaf-bearing shoots, true roots, and vascular bundles with tracheides and sieve-tubes. Fertilisation as in the Mosses. From the fertilised oosphere the leaf-bearing shoot arises, which bears on its leaves the reproductive organs, the spores, in capsule-like sporangia. From the germination of the spore a small prothallium is formed, which bears the sexual reproductive organs. Alternation of generations: I. Prothallium with organs of sexual reproduction. II. Leaf-bearing shoot with capsule-like sporangia. 3 Classes: 1. Filicinæ, True Ferns. 2. Equisetinæ, Horsetails. 3. Lycopodinæ, Club-mosses. Division IV.--=Gymnospermæ.= The vegetative organs are in the main similar to those in the 3rd Division; special shoots are modified into flowers for the service of reproduction. From the oosphere, which is fertilised by means of the pollen-tube, the leaf-bearing plant is derived; this passes the first period of its life as an embryo in the seed, and continues its development when the germination of the seed takes place. The organs corresponding to the spores of the two preceding Divisions, are called respectively the pollen-grain and embryo-sac. The pollen-grains are multicellular; i.e. they contain an indistinct prothallium. In the embryo-sac a prothallium, rich in reserve material (endosperm), with female organs of reproduction, is developed BEFORE FERTILISATION. The pollen-grains are carried by means of the wind to the ovules; these enclose the embryo-sac, and are situated on the open fruit-leaf (carpel), which has no stigma. Alternation of generations: I. Prothallium = Endosperm in ovule. II. Leaf-bearing plant, with flowers which produce the pollen-sac and ovule. 3 Classes: 1. Cycadeæ. 2. Coniferæ. 3. Gnetaceæ. Division V.--=Angiospermæ=. The members of this group are very similar to those of Division IV. The ovules are, however, encased in closed fruit-leaves (ovary), which have a special portion (stigma) adapted for the reception and germination of the pollen-grains. The pollen-grains are bicellular, but with only a membrane separating the two nuclei; they are carried to the stigma by animals (chiefly insects), by the wind, or by some other means. Endosperm is not formed till AFTER FERTILISATION. Alternation of generations in the main as in the Gymnosperms, but less distinct; while the sexual generation, the prothallium, with the organs of fertilisation, is also strongly reduced. 2 Classes:[1] 1. Monocotyledones. Embryo with one seed-leaf. 2. Dicotyledones. Embryo with two seed-leaves. For a long time the vegetable kingdom has been divided into. CRYPTOGAMS (so called because their organs of reproduction remained for some time undiscovered), and PHANEROGAMS or Flowering-plants which have evident sexual organs.