Or again, the division may be based on the fundamental parts, as follows

Cellular plants include those not furnished with fibrovascular bundles, e. g. Algæ, Fungi, and Muscineœ.

Vascular plants; furnished with fibro-vascular bundles in addition to cellular or fundamental tissue, e. g. all plants not included in the first subdivision.

The following arrangement will be followed in the present work

SUBDIVISION I.

Mycetozoa. Saprophytes. During the vegetative phase consisting of a motile plasmodium formed by the coalescence of numerous zoospores. During the reproductive stage the plasmodium becomes differentiated into spores contained within a sporangium, rarely borne on the surface of a sporophore and uncovered.

SUBDIVISION II. Thallophyta. Plants with or without chlorophyll, without any differentiation into stem and leaves, true roots and fibro-vascular bundles absent, alternation of generations not distinctly marked.

SUBDIVISION III. Muscineæ.

True roots and fibro-vascular bundles absent. Alternation of generations becoming distinctly marked in the higher forms, the sexual generation with a distinct stem bearing leaves, the oophore giving origin to the asexual generation, which consists of a sporangium containing spores.

SUBDIVISION IV. Pteridophyta. Alternation of generations distinct, disappearing in the higher forms. Fibro-vascular bundles, stem bearing leaves, and true roots present in the asexual or spore-bearing generation. Sexual generation a small prothallus.

SUBDIVISION V. Phanerogamia. The sexually-formed reproductive body a seed containing an embryo. True roots, leaf-bearing stem, and fibro-vascular bundles present. Alternation of generations obsolete.

CHAPTER II.

SUBDIVISION I.-MYCETOZOA.

Peculiarities presented during the Vegetative Phase-Characteristic Features of the Reproductive Phase-Affinities-Occurrence.

THE Mycetozoa, known also by the older names of Myxogastres and Myxomycetes, were until recently considered as belonging to the Fungi, some groups of which they superficially resemble in the mature condition; but a careful study of the life-history of several typical forms has shown that this idea is untenable, and some of the best authorities consider the group as entirely outside the Vegetable Kingdom. The species are saprophytes, and either aquatic or more generally met with on decaying wood or other vegetable matter during their vegetative condition. There are two principal groups, the Myxomycetes and the Acrasieæ.

CLASS I.-MYXOMYCETES.

The spores on germination give origin to motile cells, which are either furnished with cilia or move in an amœboid manner by the protrusion of pseudopodia. During the active period the spores multiply rapidly by division, eventually the cilia are withdrawn, and sluggish amoeboid movements only take place previous to the formation of a

plasmodium, which is accomplished as follows. Several of the cells come into contact and coalesce; this small mass possesses the power of attracting to itself other free cells,

Fig. 15.-(x 300). A, part of the naked protoplasm of Didymium leucopus, a Myxogaster, in the motile condition, during the vegetative state; the strands of protoplasm are continually changing their form, and the whole mass also moves. B, a closed sporangium of another species of Myxogaster, Arcyria incarnata. C, the same after rupture of wall of sporangium, p; cp, the expanded capillitium (x 20). From Prantl.)

which also blend to form a large mass or plasmodium that in some species extends for several inches. The plasmodium is usually if not always enclosed in a thin, yielding pellicle,

G

which gives a cellulose reaction, and still possesses the power of movement, creeping over the surface of decayed wood, etc. The most pronounced feature of the Myxomycetes is that the entire vegetative stage is passed in this condition, the motile plasmodium moving about and feeding on organic matter. During the winter the plasmodium retires into the crevices of decaying wood or amongst leaves, and under certain conditions secretes a thick wall and passes into a resting-stage. As a rule the plasmodium is bright coloured, sometimes pure white, and in the active condition is of a semi-liquid nature, so that it cannot be handled without becoming resolved into a shapeless mass resembling the white of an egg in consistency. At the end of the vegetative period the plasmodium comes to the surface of the substance amongst which it previously passed its existence, and not unfrequently creeps up the stems of grass or twigs for the purpose of forming its spores. The passage from the vegetative to the reproductive phase is abrupt : when the plasmodium has placed itself in a favourable position exposed to light, the protoplasm at once becomes converted into spore-containing bodies or sporangia, which vary considerably in form and size in different species. In the simpler forms the plasmodium becomes differentiated into a protective covering or sporangial-wall and spores only; whereas in the higher forms, in addition to the above, a portion of the protoplasm is formed into threads, often forming a network, mixed with the spores, and known as the capillitium, which in some instances is elastic and aids in the dispersion of the spores. The sporangia are often brilliantly coloured and present very beautiful shapes. When individually small, the sporangia are frequently produced in great numbers from the plasmodium, and form