290 



POSITION AND FORM OF THE EMBRYO. 



is thus reversed or inverted. Again, in an anatropal seed (figs. 493, 

 494), where the micropyle is close to the hilum, and the chalaza at 



the opposite extremity, 

 the embryo is erect or 

 homotropal (Spoto;, like, 

 and T^iTru, I turn), the 

 radicle or base of the 

 embryo being directed to 

 the base of the seed. In 

 some anatropal ovules, as 

 in Castor oil (fig. 483), 

 the exostome is thickened 

 or carunculate, c, and the 

 endostome does not correspond exactly to it, so that the radicle, e r, 

 of the embryo is directed to a point a little removed from the exostome. 

 In curved or campy lotropal seeds (fig. 419), the embryo is folded so 

 that its radicular and cotyledonary extremities are approximated, and 

 it becomes amphitropal (xp(pl, around, and Tpeira, I turn). In this 

 instance the seed may be exalbuminous, and the embryo may be 

 folded on itself (fig. 524) ; or albuminous, the embryo surrounding 

 more or less completely the perisperm, and being peripherical (fig. 

 522). In fig. 524, the seed of Erysimum cheiranthoides 

 is shown, with the chalaza, c A, and the hilum, A, nearly 

 confounded together, the micropyle, m, the embryo occu- 

 pying the entire seed, with the radicle, r, folded on the 

 cotyledons, c, which enclose the plumule, g. Thus, by 

 determining the position of the hilum, chalaza, and 

 micropyle, the direction of the embryo may be known. 



604. According to the mode in which the seed is at- 

 tached to the pericarp, the radicle may be directed up- 

 wards, or downwards, or laterally, as regards the ovary, 

 In an orthotropal ovule attached to the base of the peri- 

 carp, it is superior (fig. 521). So also in a suspended 

 525 anatropal ovule, as in fig. 483. In other anatropal ovules, 



as in figs. 492, 504, 525, the radicle is inferior. When the ovule is 

 horizontal as regards the pericarp, (fig. 523), the radicle, r, is either 



inverted. 



Fig. 524. Campylotropal seed of Erysimum cheiranthoides, cut longitudinally, m, Micropyle. 

 c ft, Chalaza not far removed from the hilum, h. t, Testa or episperm. m i, Inner covering of 

 the seed or endopleura. r, Radicle, c, Cotyledons, g, Gemmule. The embryo is curved or 

 amphitropal. 



Fig. 525. Vertical section of the carpel of Triglochin Barrelieri. p. Pericarp crowned by 

 the sessile stigma, s. g, Seed. /, Funiculus. r, Raphe. c, Chalaza. 



