214 



COMPOUND ORGANS OF PLANTS. 



rudimentary leaves are named cotyledons, and the little bud 

 by wbich the plumule is terminated, is called the gemmule, 

 (Pig. 107.) 



Before we examine in succession these four parts of the 

 embryo, let us consider their relative positions with respect to 

 the other parts of the seed. 



When albumen is present in the seed along with the embryo, 

 the embryo may either lie in its midst directly in the axis of 

 the seed as in the pansy, Viola tricolor, (Kg. 108,) when it is 

 axial ; or it may surround the albumen itself, instead of being 

 surrounded by it as in the Marvel of Peru, (Fig. 109,) when 

 it is peripherioal. In the grasses, maize, wheat and all the 

 cerealia, the embryo lies external to the albumen on one of 

 the sides of the see4, having been apparently forced into this 

 position by the irregular development of the parts of the seed, 

 when it is abaxial. (Fig. 110, Indian corn.) 



Fig. 108. Pig. 109. Fig.llO. 



Fig, 108. Vertical section of tlie seed of the Pansy. The seed is anatropal ; the em- 

 bryo homotrope. cTi, chalaza to which co, the cotyledons point; pZ, the plumule; h^ 

 the hilum; aZ, the albumen surrounding the embryo which it will be perceiTed is 

 axial ; r, the raphe connecting the hilum or base of the seed with the chalaza or base 

 of the nucleus. 



Fig. HO. Vertical section of a grain of Indian corn (Zea Mays.) r, the radicle ; p, the 

 plumule ; c, the cotyledons. 



The embryo is sometimes straight but very frequently 

 curved in a variety of ways, its curvature depending on that 



