The two large plano-convex structures are called the cotyledons or seed-leaves (Fig. 2, c), and they, together with the small peg-shaped body, constitute the embryo of the oak. The peg-shaped body presents two ends which project slightly between the two cotyledons beyond the points of attachment to them; the larger of these ends has the shape of a conical bullet, and is directed so that its tip lies in the point of the narrower part of the acorn; the other, and much smaller end, is turned towards the broader extremity of the acorn. The larger, bullet-shaped portion is termed the radicle (Fig. 2, r), and will become the primary root of the oak-plant; the smaller, opposite end is the embryo bud, and is termed the plumule (Fig. 2, pl), and it is destined to develop into the stem and leaves of the oak. If the observer takes the trouble to carefully separate the two
egg-shaped body consists chiefly of two longitudinal halves, separated by a median plane which runs through the acorn from top to bottom. These two halves, lying face to face so closely that it requires the above manipulation to enable us to detect the plane of separation (Fig. 2, l), are not completely independent, however; at a point near the narrower end each of them is attached to the side of a small peg-shaped body, with a conical pointed end turned towards the narrow end of the acorn. This tiny peg-shaped structure is so small that it may be overlooked unless some little care is exercised, but if the hard masses are completely torn apart it will be carried away with one of them.