POSITION AND FOKM OF THE EMBRYO. 



341 



without). When the embryo follows the direction of the axis of the 

 seed, it is axils or axial, and it may be either external, so as to come 

 into contact with the perisperm only by its cotyledonary apex (fig. 

 615), or internal (figs. 588, 589, 590, see p. 332). In the latter case, 

 the radicular extremity may, as in some Coniferse, become incorporated 

 with the perisperm apparently by means of a thickened suspensor. 



Fig. 616. 



Kg. 616. 



Fig. 617. 



Fig. 618. 



"When the embryo is not in the direction of the axis, it becomes 

 abawile or abaxial (fig. 616 e) ; and in this case it may be either 

 straight or curved, internal or -external. In the straight seed of 

 Grasses the perisperm is abundant, and the embryo lies at a point 

 on its surface immediately below the integuments, being straight and 

 external. In Campylotropbus ovules the embryo is curved, and in 

 place of being embedded in perisperm, is frequently external to it, 

 following the concavity of the seed (fig. 618), and becoming peripheri- 

 cal (■ffsg/psgw, I carry round), with the chalaza situated in the curva- 

 ture of the embryo. 



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, che 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 Primulacese, Plantaginacese, and many Palms, especially 

 the Date (fig. 616). The position of the embryo in difierent kinds 

 of seeds varies. In an orthotropal seed the embryo is inverted or 

 antitropal (avri, opposite, rgswiu, I turn), the radicle pointing to the 

 apex of the seed, or to the part opposite the hUum (fig. 617). Thus, 

 fig. 619 represents an orthotropal seed of Sterculia Balaoighas, at- 



Fig. 616. Grain of Carex depauperata, cut vertically, t. Integuments, p, Perisperm. 

 <!, Embryo. Fig. 616. Seed or kernel of the Date, p, Perisperm or horny albumen, e. 

 Embryo. 1, Entire seed. 2, Seed cut transversely at the point where the embryo, e, is 

 situated. Fig. 617. Winged fruit of Rumex, cut vertically to show the abaxile or abaxial 

 slightly curved embryo. Fig. 618. Carpel of Mirabilis Jalapa, out vertically, with the 

 , seed which it oontaius. a. Pericarp crowned with the remains of the style, s. t, Integu- 

 ments of the seed or spermoderm. e, Peripherical embryo, with its radicle, r, and its coty- 

 ledons, c. J), Perisperm or albumen surrounded by the embryo. 



