SECTION 15.] EMBRYO. 127 



386. The Kernel, or Nucleus, is the whole body of the seed within the 



coats. Iii many seeds the ker- 

 nel is all Embryo ; in others 

 a large part of it is the Al- 

 bumen. For example, in Fig. 

 423, it is wholly embryo; in 



Fig. 422, all but the small 420 428 421 ~422 



speck (^) is albumen. 



387. The Albumen or Endosperm of the seed is sufficiently charac- 

 terized 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 gener- 

 ally 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 re- 

 lation 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. 



390. The Cotyledons have already been illustrated as re- 

 spects their number, giving the important distinction of Dicoty- 

 ledonous, 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 Cruciferse, two 

 different modes prevail in the way the two cotyledons 

 are brought round against the radicle. In one series 

 425 426 they are 



FIG. 420. Seed of a Violet (anatropous) : a, hilum; &, rhaphe; c, chalaza. 



FIG. 421. Seed of a Larkspur (also anatropous); the parts lettered as in the last. 



FIG. 422. The same, cut through lengthwise: a, the hilum; c, chalaza; d, outer 

 seed-coat; , inner seed-coat; /, the albumen ; g, the minute embryo. 



FIG. 423. Seed of a St. John's-wort, divided lengthwise; here the whole kernel 

 is embryo. 



FIG. 424. Embryo of Calycanthus ; upper part cut away, to show the convolute 

 cotyledons. 



FIG. 425. Seed of Bitter Cress, Barbarea, cut across to show the accumbent 



cotyledons. 426. Embryo of same, whole. 



