ed (root
cut away); cotyledons well developed into foliage-leaves: succeeding
internode and leaf well developed, and the next forming. 45. Seedling
more advanced; reduced to much below natural size.]

34. Smaller embryos, less developed in the seed, are more dependent upon
the extraneous supply of food. The figures 46-53 illustrate four grades
in this respect. The smallest, that of the Peony, is still large enough
to be seen with a hand magnifying glass, and even its cotyledons may be
discerned by the aid of a simple stage microscope.

35. The broad cotyledons of Mirabilis, or Four-o'clock (Fig. 52, 53),
with the slender caulicle almost encircle and enclose the floury
albumen, instead of being enclosed in it, as in the other illustrations.
Evidently here the germinating embryo is principally fed by one of the
leaf-like cotyledons, the other being out of contact with the supply. In
the embryo of Abronia (Fig. 54, 55), a near relative of Mirabilis, there
is a singular modification; one cotyledon is almost wanting, being
reduced to a rudiment, leaving it for the other to do the work. This
leads to the question of the

36. =Number of Cotyledons.= In all the preceding illustrations, the
embryo, however different in shape and degree of development, is
evidently constructed upon one and the same plan, namely, that of two
leaves on a caulicle or initial stem,--a plan which is obvious even when
one cotyledon becomes very much smaller than the other, as in the rare
instance of Abronia (Fig. 54, 55). In other words, the embryos so far
examined are all

37. =Dicotyledonous=, that is, two-cotyledoned. Plants which are thus
similar in the plan of the embryo agree likewise in the general
structure of their stems, leaves, and blossoms; and thus form a class,
named from their embryo DICOTYLEDONES, or in English, DICOTYLEDONOUS
PLANTS. So long a name being inconvenient, it may be shortened into
DICOTYLS.

[Illustration: Fig. 46. Section of a seed of a Peony, showing a very
small embryo in the albumen, near one end. 47. This embryo detached, and
more magnified.]

[Illustration: Fig. 48. Section of a seed of Barberry, showing the
straight embryo in the middle of the albumen. 49. Its embryo detached.]

[Illustration: Fig. 50. Section of a Potato seed, showing the embryo
coiled in the albumen. 51. Its embryo detached.]

[Illustration: Fig. 52. Section of the seed of Mirabilis or
Four-o'clock, showing the embryo coiled round the out