tendril, while in the upper part it could not be told by a beginner which
was the continuation of the main stem. For these reasons I left this out
in the questions on the Pea, but it should be taken up in the class. How
are we to tell what constitutes a single leaf? The answer to this question
is that buds come in the _axils_ of single leaves; that is, in the inner
angle which the leaf makes with the stem. If no bud can be seen in the
Pea, the experiment may be tried of cutting off the top of the seedling
plant. Buds will be developed in the axils of the nearest leaves, and it
will be shown that each is a compound leaf with two appendages at its
base, called stipules, and with a tendril at its apex. 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