[Illustration: Fig. 422. The same, cut through lengthwise: _a_, the hilum; _c_, chalaza; _d_, outer seed coat; _e_, inner seed-coat; _f_, the albumen; _g_, the minute embryo.] [Illustration: Fig. 423. Seed of a St. John's-wort, divided lengthwise; here the whole kernel is embryo.] 386. =The Kernel, or Nucleus=, is the whole body of the seed within the coats. In many seeds the kernel is all _Embryo_; in others a large part of it is the _Albumen_. For example, in Fig. 423, it is wholly embryo; in Fig. 422, all but the small speck (_g_) is albumen. 387. =The Albumen or Endosperm= of the seed is sufficiently characterized and its office explained in Sect. III., 31-35. 388. =The Embryo= or _Germ_, which is the rudimentary plantlet and the final result of blossoming, and its development in germination have been extensively illustrated in Sections II. and III. Its essential parts are the _Radicle_ and the _Cotyledons_. 389. =Its Radicle or Caulicle= (the former is the term long and generally used in botanical descriptions, but the latter is the more correct one, for it is the initial stem, which merely gives origin to the root), as to its position in the seed, always points to and lies near the micropyle. In relation to the pericarp it is _Superior_, when it points to the apex of the fruit or cell, and _Inferior_, when it points to its base, or downward. [Illustration: Fig. 424. Embryo of Calycanthus; upper part cut away, to show the convolute cotyledons.] 390. =The Cotyledons= have already been illustrated as respects their number,--giving the important distinction of _Dicotyledonous_, _Polycotyledonous_ and _Monocotyledonous_ embryos (36-43),--also as regards their thickness, whether _foliaceous_ or _fleshy_; and some of the very various shapes and adaptations to the seed have been figured. They may be straight, or folded, or rolled up. In the latter case the cotyledons may be rolled up as it were from one margin, as in Calycanthus (Fig. 424), or from apex to base in a flat spiral, or they may be both folded (_plicate_) and rolled up (_convolute_), as in Sugar Maple (Fig. 11.) In one very natural family, the Cruciferæ, two different modes prevail in the way the two cotyledons are brought round against the radicle. In one series they are _Accumbent_, that is, the edges of the flat cotyledons lie against the radicle, as in Fig. 425, 426. In another they are [Illustration: Fig. 425. Seed of Bitter Cress, Barbarea, cut across to show the accumbent cotyledons. 426. Embryo of same, whole.] _Incumbent_, or with the plane of the cotyledons brought up in the opposite direction, so that the back of one of them lies against the radicle, as shown in Fig. 427, 428. [Illustration: Fig. 427. Seed of a Sisymbrium, cut across to show the incumbent cotyledons. 428. Embryo of the same, detached whole.]