parts. The end which almost touches the seed coat is caulicle, the other
end belongs to the solitary cotyledon. In germination the whole
lengthens (but mainly the cotyledon) only enough to push the proximate
end fairly out of the seed; from this end the root is formed, and from a
little higher the plumule later emerges. It would appear therefore that
the cotyledon answers to a minute leaf rolled up, and that a chink
through which the plumule grows out is a part of the inrolled edges. The
embryo of Indian Corn shows these parts on a larger scale and in a more
open state (Fig. 66-68). There, in the seed, the cotyledon remains,
imbibing nourishment from the softened albumen, and transmitting it to
the growing root below and new-forming leaves above.

[Illustration: Fig. 60. Section of an Onion seed showing the slender and
coiled embryo in the albumen, moderately magnified. 61. Seed of same in
early germination.]

[Illustration: Fig. 62. Germinating Onion, more advanced, the chink at
base of cotyledon opening for the protrusion of the plumule, consisting
of a thread-shaped leaf. 63. Section of base of Fig. 62, showing plumule
enclosed. 64. Section of same later, plumule emerging. 65. Later stage
of 62, upper part cut off. 66. A grain of Indian Corn, flatwise, cut
away a little, so as to show the embryo, lying on the albumen which
makes the principal bulk of the seed. 67. A grain cut through the middle
in the opposite direction, dividing the embryo through its thick
cotyledon and its plumule, the latter consisting of two leaves, one
enclosing the other. 68. The embryo taken out whole; the thick mass is
the cotyledon, the narrow body partly enclosed by it is the plumule, the
little projection at its base is the very short radicle enclosed in the
sheathing base of the first leaf of the plumule.]

[Illustration: Fig. 69. Grain of Indian Corn in germination, the
ascending sprout is the first leaf of the plumule, enclosing the younger
leaves within, at its base the primary root has broken through. 70. The
same, advanced; the second and third leaves developing, while the
sheathing first leaf does not further develop.]

42. The general plan is the same in the Onion (Fig. 60-65), but with a
striking difference. The embryo is long, and coiled in the albumen of
the seed. To ordinary examination it shows no distinction of parts. But
germination plainly shows that all except the lower end of it is
cotyledon. For after it has lengthe