36 BOTANY. 
omphalode, or else pass under the external integument in the form of a raphe 
to the chalaza, when this is not coincident with the hilum. The terms, 
orthotropal, campylotropal, anatropal, face, back, &c., already explained 
under the head of the ovule, apply equally to the seed. | 
As the embryo increases in size, it causes an absorption of cellular matter 
from the embryo sac and nucleus, to such an extent as sometimes to reduce 
these to the condition of a thin integument, in which case the seed consists 
of embryo and integuments alone. A peculiar substance, termed albwmen, 
is frequently formed around the embryo, which, when developed within the 
embryo-sac alone, is known as endospermic albwmen, or endosperm ; and 
when within the cells of the nucleus alone, perispermic albumen, or peris- 
perm. Sometimes both kinds occur in the same seed: when the embryo 
occupies the whole seed, this is exalbuminous ; albwminous, when there is a 
separate deposit of albumen. The object of the albumen is to supply food to 
the embryo at the period of germination. It varies much in its nature, bemg 
farinaceous, or mealy, consisting of starchy cells, as in the grains ; fleshy, or 
cartilaginous, as in the cocoa-nut ; and horny, as in some palms, and in coffee. 
When the cellular tissue combines with the albuminous matter so completely 
as to form but one substance, the albumen is solid ; ruminated, when a portion 
of the tissue remains unconverted, causing a mottled appearance, as in the 
nutmeg. The albumen consists, chemically, of oily matter, starch, and 
nitrogenized compounds. ; 
The embryo consists of cotyledons, or rudimentary leaves; the plumule, 
or gemmule, which represents the ascending axis; the radicle, or the germ 
of the descending axis; and the point of union. of the two, or the collum. 
The part intervening between the collar and cotyledons is the caulicule, or 
tigelle. The embryo varies in its structure in different divisions of the 
vegetable kingdom. Thus, in acrogens and thallogens it continues to be a 
cell or spore, with granular matter in the interior, without any cotyledons ; 
hence such plants are said to be acotyledonous. In endogens and exogens, 
on the other hand, there is a distinct separation of parts in the embryo, the 
former having, however, but one cotyledon (monocotyledonous), the latter 
two (dicotyledonous). In the spore of the acotyledonous plant germination 
takes place in any part of the surface. Sometimes spores are united in 
definite numbers by a cellular covering, called perispore, or sporidiwm ; the 
_tetraspore of the Algz consists of four spores thus united. - 
The first part formed in the embryo is the azis, having one of its 
extremities turned towards the suspensor, and indicating the point whence 
the radicle is to proceed; the other end pointing in the opposite direction, 
and answering to the stem. From the point where the cotyledons are 
united to the axis a bud is developed (as from the axils of leaves); this 
contains the rudiments of the true or primordial leaves of the plant, and is 
known as the gemmule, or plumule. This bud may usually be seen lying 
within the cotyledons. In the monocotyledon the gemmule is usually 
inclosed by the mostly cylindrical cotyledon at its lower portion. The form 
of the dicotyledonous embryo varies considerably, but is always distin- 
guishable from the monocotyledonous by a division at the cotyledonary 
36 
