474 



BOTANY 



The SEED-COAT presents great variety in its appearance. It is 

 always constructed to protect the tender parts within against drying or 

 injury, and usually shows layers of cells with their walls thickened 

 and lignified or suberised. On the outside of the seed-coat the scar 

 of the funiculus can be distinguished, and is known as the HILUM ; the 

 MICROPYLE can also be seen, and in anatropous seeds the RAPHE mark- 

 ing the line of union between the funiculus and the integument, and 

 extending from the hihim to the chalaza. In some cases an ARILLUS is 

 developed from the funiculus ; this is a succulent and usually brightly 

 coloured structure, and stands in relation to the dispersal of the seed by 

 animals. An outgrowth surrounding the micropyle is found in some 



A v 



FK;. 435. .1. Seed of Hyoscyamus niger, showing 

 the dicotyledonous embryo embedded in the 

 endosperm ; B, seed of Elettaria Cardamoimim, 

 enveloped by a thin aril ; the white, mealy 

 perisperm next to the seed - coat encloses 

 an oleaginous endosperm (shaded), in which 

 the monocqtyledonous embryo lies embedded. 

 (After BERG and SCHMIDT.) 



Fio. 436. Capsflla burssa pastoris. A, Longi- 

 tudinal section of a ripe seed; /(, hypocotyl; 

 c, cotyledons ; v, vascular bundle of thr 

 funicle(x 26); B, longitudinal section of 

 the seed-coat after treatment with water ; 

 t, the swollen epidermis; o, brown, strongly 

 thickened layer ; *, compressed layer of 

 cells ; a, the single porsisting layer of 

 endosperm cells containing alem-onc grains 

 (x 250). 



seeds, especially those of the Euphorbiaceae, and is termed a CARUN- 

 CULA (Figs. 437, 438). 



The effect of fertilisation is not only seen in the macrosporangia 

 but extends to the macrosporophylls or carpels. The structures of 

 very various form which are formed from the carpels (often together 

 with the persistent calyx and the floral axis) are called FRUITS, and 

 serve primarily to protect the developing seeds. The different forms 

 of fruit will be frequently referred to in the special accounts of the 

 classes and orders below. 



The GERMINATION of the seed, i.e. the resumption of growth at the 

 end of the resting period, must also be briefly considered. The chief 

 condition of germination is the absorption of water. The embryo 

 resumes its growth, which has for a time been arrested, ruptures the 

 seed-coat and sends its root down into the soil. When it is in this 

 way firmly fixed in position the cotyledons become free from the 

 seed and expand in the light ; when they remain within the seed- 



