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.

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.

The first three divisions belong to the Cryptogams, and the third and fourth divisions to the Phanerogams. This arrangement has no systematic value, but is very convenient in many ways.

The Cryptogams are also known as Spore-plants, since they multiply by unicellular organs (spores), and the Phanerogams in contradistinction are called Seed-plants (Spermaphyta), since they multiply by seeds, multicellular bodies, the most important part of which is the embryo (a plant in its infancy). Mosses, Ferns, and Gymnosperms are together known as Archegoniatæ, since they possess in common a female organ of distinct structure, the Archegonium.

DIVISION I.
THALLOPHYTA.

The thallus in the simplest forms is unicellular; in the majority, however, it is built up of many cells, which in a few instances are exactly similar; but generally there is a division of labour, so that certain cells undertake certain functions and are constructed accordingly, while others have different work and corresponding structure. Vessels or similar high anatomical structures are seldom formed, and the markings on the cell-wall are with few exceptions very simple. The Myxomycetes occupy quite an isolated position; their organs of nourishment are naked masses of protoplasm (plasmodia).

As regards the external form, the thallus may be entirely without special prominences (such as branches, members), but when such are present they are all essentially alike in their origin and growth, that is, disregarding the hair-structures which may be developed. A shoot of a Seaweed or of a Lichen, etc., is essentially the same as any other part of the plant; only among the highest Algæ (Characeæ, certain Siphoneæ, Sargassum, and certain Red Seaweeds) do we find the same differences between the various external organs of the plant body as between stem and leaf, so that they must be distinguished by these names.

Roots of the same structure and development as in the Seed-plants are not found, but organs of attachment (rhizoids and haptera) serve partly the biological functions of the root.

Systematic division of the Thallophytes. To the Thallophytes belong three sub-divisions—Slime-Fungi, Algæ, and Fungi. Formerly the Thallophytes were divided into Algæ, Fungi, and Lichens. But this last group must be placed among the Fungi, since they are really Fungi, which live symbiotically with Algæ. The Slime-Fungi must be separated from the true Fungi as a distinct subdivision. The Algæ possess a colouring substance, which is generally green, brown, or red, and by means of which they are able to build up organic compounds from carbonic acid and water. The Bacteria, especially, form an exception to the Algæ in this respect; like the Fungi and Slime-Fungi they have as a rule no such colouring material, but must have organic carbonaceous food; these plants form no starch, and need no light for their vegetation (most Fungi require light for fructification). The Myxomycetes, Bacteria, and Fungi derive their nourishment either as saprophytes from dead animal or vegetable matter, or as parasites from living animals or plants (hosts), in which they very often cause disease.