Buds can be forced
in the same way to grow from the axils of the lower scales, and even from
those of the cotyledons, and the lesson may be again impressed that organs
are capable of undergoing great modifications. The teacher may use his own
judgment as to whether he will tell them that the tendril is a modified
leaflet.
[Illustration: FIG. 9. 1. Grain of Indian Corn. 2. Vertical section,
dividing the embryo, _a_, caulicle: _b_, cotyledon; _c_, plumule. 3.
Vertical section, at right angles to the last.]
6. _Monocotyledons_.--These are more difficult. Perhaps it is not worth
while to attempt to make the pupils see the embryo in Wheat and Oats. But
the embryo of Indian Corn is larger and can be easily examined after long
soaking. Removing the seed-covering, we find the greater part of the seed
to be albumen. Closely applied to one side of this, so closely that it
is difficult to separate it perfectly, is the single cotyledon. This
completely surrounds the plumule and furnishes it with food from the
albumen. There is a line down the middle, and, if we carefully bend back
the edges of the cotyledon, it splits along this line, showing the
plumule and caulicle within. The plumule consists of successive layers of
rudimentary leaves, the outer enclosing the rest (Fig. 10, 1, _c_). The
latter is the first leaf and remains undeveloped as a scaly sheath (Fig.
10, 2, _c_). In Wheat and Oats the cotyledon can be easily seen in the
largest seedlings by pulling off the dry husk of the grain.
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