The living medium, then, which possesses the marvellous property of being primarily aroused into life and energy, and which either forms the whole or the greater portion of every plant, is in its earliest and simplest form nothing more than a microscopic cell, consisting of one or two colourless particles of matter, in closest contact, and wholly immersed in a transparent substance somewhat resembling _albumen_ (white of egg), termed _protoplasm_, but differing essentially in its character and properties. This nearly colourless organisable matter is the life-blood of the cell. It is sufficiently viscid to maintain its globular form, and under high powers is seen to have a slightly consolidated film enclosing semi-transparent particles, together with vacuoles which are of a highly refractive nature. These small bodies are termed nuclei, and they appear to be furnished with an extremely delicate enveloping film. In a short time the nuclei increase in number and split up the parent body. The protoplasmic mass, however, is undoubtedly the true formative material, and is rightly regarded as “the physical basis of life” of both the vegetable and animal kingdoms. There are, however, certain members of the vegetable kingdom which somewhat resemble animals in their dependence upon receiving organic compounds already formed for them, being themselves unable to effect the fixation of the carbon needed to effect the first stage in their after chemical transformations. Such is the case with a large class of flowering plants, among Phanerogams, and the leafless parasites which draw their support chiefly from the tissues of their hosts. It is likewise the case with regard to the whole group of fungi; the lower cryptogams, which derive the greater portion of their nutritive materials from organic matter undergoing some form of histolysis; while others belonging to this group have the power of originating decomposition by a fermentative (_zymotic_) action peculiarly their own. There are many other protophytes which live by absorption, and which appear to take in no solid matter, but draw nourishment from the atmosphere or the water in which they exist. With regard to motion, this was at one time considered the distinctive attribute of animal life, but many protophytes possess a spontaneity of power and motion, while others are furnished with curious motile organs termed _cilia_, or whip-like appendages, _flagella_, by which their bodies are propelled with considerable force through the water in which they live.