[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. The food will he seen to have been used up.
[Illustration: FIG. 10. 1. Germination of Indian corn. 2. Same more advanced. a, caulicle; c1, first leaf of the plumule, sheathing the rest; c2, second leaf; c3, third leaf of the plumule; d, roots.]
The series of Corn seedlings, at least, should be drawn as before and the parts marked, this time with their technical terms. The following questions should then be prepared.
CORN.
What are the parts of the seed?
Compare these parts with the Morning-Glory, Sunflower, Bean, and Pea.
Where is the food stored?