264 



MANUAL OF BOTANY 



Fig. 577. 



body commonly called the embryo. We may have thus thi-ee 

 distinct generations represented in the seed. 1. The megaspore 

 and the remains of the original megasporangium, or the nucellus 

 of the ovule with its integuments. The latter are frequently the 

 only part of the sporangium remaining, the nucellus itself having 

 disappeared. 2. The gametophyte, consisting of a mass of tissue 

 called the endosperm, developed inside the spore or embryo-sac. 

 This again is frequently only represented very slightly, or it may 

 be altogether absent, having been absorbed by the embryo. 

 3. The new sporophyte, or embryo, which may be small and 

 embedded in the endosperm, or maybe large, filling the embryo- 

 sac, having absorbed the endosperm during its development. 

 If the nucellus also has been absorbed during the growth of 

 the embryo-sac, the seed may present to view only the em- 

 bryo enveloped in the modified original integuments of the 

 megasporangium or ovule. 



Like the ovule, the seed is either at- 

 tached to the placenta directly, in which 

 case it is described as sessile ; or by means 

 of a stalk, called the funiculus or funicle 

 {figs. 512, /, and 577, /), when it is said 

 to be stalked ; its point of attachment is 

 termed the hilum. The position of this 

 hihim may be commonly seen on seeds 

 which have separated from the ftuiioulus 

 or placenta, by the presence of a scar, or by 

 a. difference of colour to the surrounding 

 integument. The hilum varies much in 

 size, being in some cases very minute, but 

 in others extending for some distance over 

 the surface of the outer coat of the seed, 

 as in the Horsechestnut and Calabar Bean. 

 The hilum, as in the ovule, indicates the 

 base of the seed. The chalaza is well seen 

 in the Orange, and commonly in all anatro- 

 pous seeds, in which case also the raphe may 

 be generally noticed forming a projection 

 on the face of the seed. 



The micropyle also, although smaller and less distinct 

 than in the ovule, owing to a contraction of the surrounding 

 parts, may be frequently observed in the seed ( fig. 511, m) ; 

 its detection is of some practical importance, as the radicle, 

 r, of the embryo, with a few exceptions, is directed towards it. 



Fig. 677. The seed of a 

 Pea, with its integu- 

 meDts removed on one 

 side. pi. Placenta. /. 

 Funiculus, rap. Eaphe, 

 cji. Chalaza. m. Micro- 

 pyle. te. Testa or epi- 

 sperm. e. Endopleura 

 or tegmen. The part 

 within the endopleura 

 is commonly called the 

 nucleus of the seed,and 

 is formed of cotyle- 

 dons, c, gemmule or 

 plumule, (7, radicle, r, 

 aud ( stalk or tigellum 

 between the plumule 

 and radicle. 



