The GYMNOSPERMS go still further. The macrospore (embryo-sac) germinates and forms internally a cellular tissue, designated in former times by the name of _albumen_ (endosperm), which is _homologous with the prothallium_. It always _remains enclosed in the embryo-sac_, and is a parenchymatous mass containing a large supply of nourishment. In the upper part of the endosperm a number of archegonia are developed which are in the main constructed in the same manner as those in the Cryptogams, but are still more reduced, the neck consisting only of 4, 2, or 1 cell (Figs. 251, 252). The ventral canal-cell is also formed, in the majority, as a small portion cut off from the large central cell just beneath the neck; the larger remaining portion becomes the oosphere. When the pollen-tube has passed down to the oosphere (Fig. 253) and fertilisation has been effected, the oospore commences a cell-formation, the final result of which is the formation of _an embryo_ (_the asexual generation_) which is provided with a thinner, lower end, termed the suspensor. The embryo is forced more or less into the endosperm in which it may rest for a longer or shorter time, and generally is developed to such an extent that it has a distinct primary-root (radicle) and stem (plumule) with one or more embryo-leaves (cotyledons). When the oosphere has been fertilised its nucleus sinks down to its lower end, and by repeated division into two, forms four cells lying in one plane (Fig. 253, see base of the left archegonium). Three tiers of cells are now formed by transverse division of these four. It is the intermediate one of these which elongates and forms the suspensor, or four suspensors, if they separate from each other, which push the lowermost four cells deep down into the endosperm. It is from these four lower cells that the embryo (or four embryos when the suspensors separate) is developed, but never more than one embryo attains full development. As several archegonia are contained in one and the same ovule, all of which are capable of forming embryos, there is the possibility that several embryos may be developed in a seed (polyembryony), but usually only one embryo attains perfect development. [Illustration: FIG. 253.--The apex of the nucellus (_n_) of _Abies_ in longitudinal section: _c_, _c_ the oospheres of the two archegonia; the embryo-formation has commenced at the bottom of the left archegonium; _s_ wall of the macrospore; _p_ pollen-grains; _r_ pollen-tubes.] [Illustration: FIG. 254.--Embryo-sac of _Carex præcox_: _syn_ synergidæ; _kb_ the oosphere; _c_ the central nucleus; _ant_ the antipodal cells.]