THE SEED. 



157 



the coats or imbedded in perisperm, exhibits many varieties in the 

 relative position of its parts : thus it may be straight (fig. 314), curved, 

 arcuate, or hooked (fig. 325), spirally coiled (fig. 326), or folded; in 



Fig. 323. 



Fig. 324. 



Fig. 325. 



Fig. 326. 



Fie. 323. Aperispermic Monocotyledonous seed of Potamoyeton, with the coat removed: 



a, radicle ; 6, cotyledon; c, plumu 1 *?. 

 Pig. 324. Embryo of Pinus, extracted from the perisperm, and the cotyledonary lobes 



separated . 



Fie 325. Vertical section of the seed of Atropa Belladonna. 

 Fig 326.' Vertical section of the seed of the Hop (Humulus). 



the last case the radicle may be folded against the back of one of the 

 cotyledons (incumbent, fig. 327) or against their edges (accumbenf). 

 The cotyledons, which are usually of fleshy texture, and vary 

 much in form, degree of expansion, and solidity in different cases, 

 are occasionally rolled or folded up like leaves in leaf -buds (figs. 

 328 & 329) ; and these are described by the terms defined above 

 under the vernation of leaves (p. 73). They are sometimes folia- 

 ceous, as in Convolvulus or Ricinus (fig. 320), &c. The fleshy 

 kinds occasionally cohere very firmly in Dicotyledons in the mature 

 state ; and they are sometimes of unequal size, as in Trapa natans. 



Fig. 328. 



Fig. 329. 



Fig. 327. Vertical section of the seed of Eryximum: a.funiculus. 

 Fig. 328! Dicotyledonous embryo extracted from a Turnip-seed. 

 Fig. 329. Dicotyledonous embryo extracted from the seed of the Maple (Acer). 



Generally the cotyledons form the greater part of the embryo, as in the 

 Bean (tig. 321) ; but sometimes they are very small or undistinguishable. 

 They usually die away, but in Welwitschia they remain to form the only 

 leaves the plant has. 



Eelative Position of the Embryo. The embryo may be in the very 

 centre of the perisperm (Polyyomim), excentric ; completely external 

 (Grasses, fig. 315) ; curved round the outside .peripherical (Lychnis, fig. 

 317). The radicle generally points to the hilum (homoblastic), rarely 

 away from it (enantioblastic). 



