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In a few weeks the ovary and its cupule have increased considerably in size, and the one successful ovule, with the rapidly developing embryo in the embryo-sac in its interior, occupies nearly the whole of its cavity; the remains of the two aborted chambers and

Fig. 36.—Sections of acorns in three planes at right angles to one another. A, transverse; B, longitudinal in the plane of the cotyledons (l); C, longitudinal across the plane of the cotyledons; c, cotyledons; t, testa; p, pericarp; s, scar, and r, radicle; pl, plumule. The radicle, plumule, and cotyledons together constitute the embryo. The embryonic tissue is at r and pl. The dots in A, and the delicate veins in B and C, are the vascular bundles.

the five unsuccessful ovules being traceable as tiny, shriveled remnants in one corner. The walls of the ovary then gradually change into the polished brown walls (pericarp) of the fruit; the walls of the ovule become the coat (testa) of the seed; and the embryo developed from the fertilized egg-cell fills up the interior of the latter, as described in Chapter II.

The ripe fruit is the acorn, and we may regard it apart from the cupule; it contains the seed.