134 



ACADEMIC BOTANV. 



IV. Centrifugal when it points to the circumference, as in the 

 Violet (Fig. 204) and Fly-trap (Pig. 179, D) ; 



V. Vague, Excentrie, when it has no definite direction, as in the 

 Primrose (Fig. 189, D). 



Flo. , 189.— A, vert. sec. of fr. of Dock (Rmnex). B, do. of fr. of Prett.y-by- 

 night (MirabilU jalapa). C, do. of sd. of CUfus gymp/iitifolius. D, do. of sd. 

 of Primrose {Primula elalior): «, embryo; h, hilum ; f, tegmen abd testa; 

 Py perispeiTQ. 



307. The position of the embryo in regard to the Seed. — The three 

 typical positions of the ovule being known, we have the following 

 positions for the embryo : I. Ovule orthotropous, embryo nraiifropoas/ 

 that is, the radicle and micropyle turned from the hilum (Fig. 189, A) ; 

 II. Ovule anatropous, embryo homotropous ; that is, the radicle and 

 micropyle turned towards the hilum (Fig. 193, B) ; III. Ovule cam- 

 pylotropous, embryo amphitropous, or bent (Fig. 189, B). IV. The 

 embryo is heterotropous when, from the unequal growth of the seed- 

 coats, neither extremity corresponds to the hilum, and the radicle no 

 longer points to the micropyle. This unusual form is found in the 

 Primrose (Fig. 18fl, D), in which the axis of the embryo is parallel to 

 the plane of the hilum ; and in the Grasses (Fig. 6, A), in which it is 

 oblique. The radicle is in these cases termed excentrie. 



308. The embryo is awUe when its axis corresponds with 



the axis of the 



whether it be straight 

 (Fig. 189, A) or curved 

 (Fig. 189, C) ; it is peri- 

 pheric when it follows the 

 periphery (circumference), 

 as in the Pretty-by-night 

 (Fig. 189, B); it is <mns- 

 verse when at right angles 

 with the axis (Fig. 189, 

 D). 



309. The Radicle and 

 Caulicle are usually small. 

 Very often, however, the caulicle is conspicuous. In the Pines (Fig. 



Tig. 190 —A, emb. of Pondweed (F^tamogelon 

 perfolialus) ; r, radicle ; t, caulicle ; c, cotyle- 

 don ; g, plumule. B, emb. of South American 

 Butternut (Caryocar butproB7nn, Pekea butyroaa). 

 C, emb. of Dodder (OusctUa Epilimum). 



