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Hazel-nut; or horny, as in the Date and Coffee. Sometimes it is not present, the testa then enclosing the embryo alone, and the seed is said to be exalbuminous, as in the Bean and Almond. The embryo is formed of a radicle and plumule, the rudiments respectively of the root and stem of the future plant, and the cotyledons, which eventually become its first or seed-leaves. In Exogens these cotyledons are generally two in number; but in a few instances several are situated in a whorl around the plumule. In Endogens there is only one present; and the plumule, usually hidden by it while in the seed, rises, after germination, from a small slit at its base. These two great divisions of the flowering plants have, from this circumstance, been also termed Di-cotyledons and Mono-cotyledons. The embryo being frequently very minute, it is often difficult to distinguish its nature until after germination; its two principal forms may be better understood by reference to the Plate. Fig. 13 represents a Bean with its testa and one of the cotyledons removed, showing the other with the small plumule and radicle at its base. Fig. 14 is the young plant after germination has taken place: the testa is thrown off; the cotyledons have expanded; and the radicle is extended downwards into the ground. Fig. 15 is a section of a grain of Wheat, a monocotyledonous seed, with the embryo lying on one side of the farinaceous albumen, which here forms the principal contents of the testa. In fig. 16 the grain has germinated; and the single, long, pointed cotyledon is rising, the plumule emerging from the slit at its base, while the radicle is extending in the contrary direction. The form and position of the embryo, however, vary very much in both monocotyledonous and dicotyledonous plants, and afford to the systematic botanist a most valuable point of distinction between different families. At that part of the seed where it is attached to the funiculus, a small scar is always found, called the hilum,—while at some point of its surface a pore exists, termed the foramen or micropyle, the opening through which the radicle is eventually protruded. The position
