POSITION AND FORM OF THE EMBRYO. 



289 



and in this case it may be either straight or curved (fig. 521), internal 

 or external. In the straight seed of Grasses, the perisperm is abun- 

 dant, and the embryo lies at a point on its surface, immediately below 



the integuments, being straight and external. In Campylotropous 

 ovules, the embryo is curved, and in place of being imbedded in peri- 

 sperm, is frequently external to it, following the concavity of the seed 

 (fig. 522), and becoming peripherical (vs^Kfs^a, I carry round), with 

 the chalaza situated in the curvature of the embryo. 



603. It has been already stated, that the radicle of the embryo is 

 directed to the micropyle, and the cotyledons to the chalaza. In some 

 cases, by the growth of the integuments, the former is turned round 

 so as not to correspond with the apex of the nucleus, and then the 

 embryo has the radicle directed to one side, and is called excentric, as 

 is seen in PrimulaceaB, Plantaginacese, and many Palms, especially the 

 Date (fig. 520). The position of the embryo in different kinds of seeds 

 varies. In all cases the radicle or base of the embryo points more or 

 less directly to the micropyle, while the cotyledonary extremity is 

 directed towards the chalaza. In an orthotropal seed, then, the em- 

 bryo is inverted or antitropal vrt, opposite, r^ina, I turn), the radicle 

 pointing to the apex of the seed, or to the part opposite the hilum 

 (fig. 521). Thus, fig. 523 represents an orthotropal seed of Sterculia 

 Balanghas, attached to the pericarp, p c, by the funiculus, f. The 

 chalaza and hilum are confounded together at c h, the micropyle being 

 at the opposite end. The integuments of the seed, i, cover the embryo 

 with its perisperm, ps; the cotyledons, c, point to the hilum and 

 chalaza ; while the radicle, r, points to the micropyle, and the embryo 



Fig. 519. Grain of Carex depauperata, cut vertically, t, Integuments, p, Perisperm. e, 

 Embryo. 



Fig. 520. Seed or kernel of the Date, p, Perisperm or horny albumen, e, Embryo. 1. En- 

 tire seed. 2. Seed cut transversely at the point where the embryo, e, is situated. 



Fig. 521. Winged fruit of Ruinex, cut vertically, to show the abaxile or abaxial slightly 

 curved embryo. 



Fig. 522. Carpel of Mirabilis Jalapa, cut vertically, with the seed which it contains, , Peri- 

 carp crowned with the remains of the style, . t, Integuments of the seed or spermoderm. 

 e, Peripherical embryo with its radicle, r, and its cotyledons, c. p, Perisperm or Albumen sur- 

 rounded by the embryo. 



U 



