XII 
Hazel-nut; or horny, as in tlie 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 respect¬ 
ively 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-coty¬ 
ledons. 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 ex¬ 
tending 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 
