leaves are mere scales,
the third begins to serve as foliage; the next more so.]

28. This _hypogaeous_ germination is exemplified on a larger scale by the
Oak (Fig. 36, 37) and Horse-chestnut (Fig. 38, 39); but in these the
downward growth is wholly a stout tap-root. It is not the caulicle; for
this lengthens hardly any. Indeed, the earliest growth which carries the
very short caulicle out of the shell comes from the formation of
foot-stalks to the cotyledons; above these develops the strong plumule,
below grows the stout root. The growth is at first entirely, for a long
time mainly, at the expense of the great store of food in the
cotyledons. These, after serving their purpose, decay and fall away.

[Illustration: Fig. 36. Half of an acorn, cut lengthwise, filled by the
very thick cotyledons, the base of which encloses the minute caulicle.
37. Oak-seedling.]

[Illustration: Fig. 38. Half of a horse-chestnut, similarly cut; the
caulicle is curved down on the side of one of the thick cotyledons. 39.
Horse-chestnut in germination; foot-stalks are formed to the cotyledons,
pushing out in their lengthening the growing parts.]

29. Such thick cotyledons never separate; indeed, they sometimes grow
together by some part of their contiguous faces; so that the germination
seems to proceed from a solid bulb-like mass. This is the case in a
horse-chestnut.

30. =Germinating Embryo supplied by its own Store of Nourishment=, i. e.
the store in the cotyledons. This is so in all the illustrations thus
far, essentially so even in the Flax. This nourishment was supplied by
the mother plant to the ovule and seed, and thence taken into the embryo
during its growth. Such embryos, filling the whole seed, are
comparatively large and strong, and vigorous in germination in
proportion to the amount of their growth while connected with the parent
plant.

31. =Germinating Embryo supplied from a Deposit outside of Itself.= This
is as common as the other mode; and it occurs in all degrees. Some
seeds have very little of this deposit, but a comparatively large
embryo, with its parts more or less developed and recognizable. In
others this deposit forms the main bulk of the seed, and the embryo is
small or minute, and comparatively rudimentary. The following
illustrations exemplify these various grades. When an embryo in a seed
is thus surrounded by a white substance, it was natural to liken the
latter to the white of an egg, and the embryo o