SECTION 15.] 



EMBKYO. 



127 



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

 coats. In many seeds the ker- 

 nel is all Embryo; in others 

 a large part of it is the Al- 

 bumen. Tor example, in Fig. 

 423, it is wholly embryo; ia 

 Fig. 422, all but the small 

 speck (g) 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 hare 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 



J0 ^~y are brought round against the radicle. In one series 



425 426 they are 



Fiq. 420. 



Fig. 421, 



Pig. 422. 

 seed-coat; 



Fig. 423, 

 is embryo. 



Fig. 424. 

 cotyledons. 



Fig. 425. 

 cotyledons. 



Seed of a Violet (anatropous) : a, hilum; b, rhaphej c, chalaza. 

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

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

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

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



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



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

 426. Embryo of same, whole. 



