The contents of the pollen grains consist of a liquid containing mucilaginous granules, which is in circulation. The granules increase in number towards the period of maturation, mingled with oil globules, and frequently starch. The circulation of the fluid ceases long before maturation in all cases, except the Zostera; but the granules of the contents exhibit an active molecular motion often within the pollen cell, and always after expulsion even in pollen taken from dried specimens. After the liquid ceases to circulate, it becomes concentrated and contracted; and when the pollen is only enclosed in one delicate membrane, it simply bursts the vesicle; but, as most pollen grains have a double coat, they burst open at the slits, or pores, on their surface, and through these the internal membrane, in the form of a tube, is protruded, and emits its contents; but it may be projected to a considerable distance without bursting. The pistil in a very young state is a greenish concave body scarcely to be distinguished from a nascent leaf; it becomes more concave; and finally the borders meet and unite, so that a hollow body is formed, which ultimately becomes a perfect pistil consisting of three parts, the apex or stigma, the style, and the ovary, in which the ovules, or unripe seeds, are formed and fertilized, the latter afterwards becoming the fruit. The ovary is composed of an outward skin containing cellular tissue and vascular bundles of spiral vessels, which, running upwards, converge towards the style; they vary in number, and are sometimes ramified. A single ovule, which is an unripe seed, may be produced within the ovary, or the ovary may be divided into two or more compartments, in each of which an ovule may be formed and attached to the ovary by a mass of cellular tissue, and not unfrequently by a single thread. The style, when examined with a microscope, is a hollow tube, or canal, extending from the cavity of the ovary to the stigma. It consists of cellular tissue with vascular bundles near the circumference, which pass upwards in straight lines, and end below the summit. In certain cases the canal is open; in others it is obstructed by lax cellular tissue having many gaps. The stigma is an expansion of that lax tissue at the point where the canal opens externally. At the time of fructification, the canal of the style is occupied by soft humid elongated cells mixed with a viscous fluid, which exudes upon the surface of the stigma, rendering it moist and glutinous. When the pollen grains adhere to that humid substance, the tubular extension of their inner lining, with its contents, passes down the style and fertilizes the unripe seeds.