Page:The Oak.djvu/152

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134
THE OAK.

straight embryo (Fig. 36, t). At the broad end the funicle can be observed attaching the seed to the base of the acorn; it is inserted laterally, and traces of the aborted ovules may sometimes be found at the point of insertion. The vessels from the funiculus branca at the chalaza and ramify in the testa.

The testa is a shining, pale-brown or yellowish skin, consisting only of a few rows of cuboidal, thin-walled parenchyma cells, the outer rows of which may be the integuments, and the innermost possibly belong to the remains of the nucellus; or the latter may be represented by the outer portion of the thin membrane which includes all that remains of the embryo-sac. A few feeble vascular bundles run through the testa (Fig. 37, g).

The testa is closely applied to the surface of the two stout cotyledons. These fill up by far the greater part of the space inclosed by the thin testa and pericarp, and their shape is almost described in saying that. Each is a colorless, hard, plano-convex body, face to face with the other by the flat surface (Fig. 36); a transverse section of the acorn shows each cotyledon occupying half the circle. At the more pointed end of the acorn these two cotyledons will be found to be joined to the very small embryo (plumule and radicle) by what will on germination lengthen into very short stalks (petioles), but which are at present mere bridges of tissue, across which minute vascular bundles run from the embryo into the cotyledons. If the shell-like investments de-