CHAPTER VI
SEEDS AND GERMINATION
The seed contains a miniature plant, or embryo. The
embryo usually has three parts that have received
names: the stemlet, or caulicle; the seed-leaf, or cotyledon
(usually 1 or 2); the bud, or plumule, lying between or
above the cotyledons. These parts are well
seen in the common bean (Fig. 15), particularly
when the seed has been soaked for a
few hours. One of the large cotyledons—comprising
half of the bean—is shown at
R. The caulicle is at O. The plumule is
shown at A. The cotyledons are attached
to the caulicle at F: this point may be taken as the first node or joint.
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Fig. 15.—Parts of the Bean.
R, cotyledon; O, caulicle; A, plumule; F, first node.
The Number of Seed-leaves.—All plants having two seed-leaves belong to the group called dicotyledons. Such seeds in many cases split readily in halves, e.g. a bean. Some plants have only one seed-leaf in a seed. They form a group of plants called monocotyledons. Indian corn is an example of a plant with only one seed-leaf: a grain of corn does not split into halves as a bean does. Seeds of the pine family contain more than two cotyledons, but for our purposes they may be associated with the dicotyledons, although really forming a different group.
These two groups—the dicotyledons and the monocotyledons—represent two great natural divisions of the vegetable kingdom. The dicotyledons contain the woody
