Page:The Oak.djvu/153

 above are removed from the embryo, it is then possible to gently separate the cotyledons and see the minute plumule and radicle to which they are joined (Fig. 36); on removing one cotyledon the plumule will be seen imbedded in a slight depression at the base. At this point there is a little room to spare, not quite filled up by the radicle and plumule; a minute remnant of endosperm may occasionally be found here, not having been entirely absorbed by the developing embryo.

The cotyledons and embryo are composed of a delicate epidermis inclosing the whole (Fig. 37, e), and very thin-walled cells forming the main mass of tissue in which the vascular bundles run. These bundles are scattered in the thickness of the cotyledons, ready to convey fluids to and fro on germination, and already contain lignified vessels in the xylem and sieve-tubes in the phloëm.

The iso-diametric, closely-packed cells of the cotyledons are filled with reserve materials, consisting of large quantities of starch grains imbedded in proteids and tannin. Here and there are scattered cells filled with brown pigments and containing tannin; some cells also contain oil-drops. Traces of sugar (quercite), certain bitter principles, acids, and mineral substances also occur in the tissues.