DICOTYLEDONOUS SEED.- GERMINATION. 



285 



FIG. 87. SEED OF THE BEAN, 



of all Monocotyledonous plants ; and also in some Dicotyledons, 

 as the Ash and Horse-chesnut. 



440. The structure of the seed . of 

 the two principal divisions of the 

 Phanerogamia, is shown in the adjoining 

 figures. In Fig. 87, is seen that of the 

 Bean, a Dicotyledon, after the seed- 

 coats have been stripped off, and the 

 cotyledons separated. The two large 

 fleshy lobes, a, #, are the cotyledons, 

 into which the whole of the starch, 

 originally contained in the ovule, has with "* cotyledons ; a, a, sepa- 



* ' rated ; b, germ. 



been absorbed. Between these is the 



real germ ; the upper extremity of which, termed the plumula, 

 subsequently developes itself into the stem, and puts forth leaves ; 

 whilst the lower part, which is always 

 c directed towards the foramen, becomes the 

 root. The plumula sometimes presents the 

 appearance of the plant in miniature; its 

 leaves and buds being quite discernible, 

 though on a very small scale. The subsequent 

 development of the germ contained in the 

 seed into the perfect plant, is that which 

 in its early stage is known as germination. 

 Of the causes which excite it, we shall 

 presently speak. When a seed like that of 

 the Bean begins to germinate, it first swells 

 and bursts its seed-coats ; the plumula then 

 extends upwards, bringing the cotyledons 

 just above the surface of the ground ; whilst 

 the radicle penetrates it in the opposite direc- 

 tion. In some plants, however, the cotyledons 

 FIG. 88. remain underground, as in the Oak ; and 



GERMINATION OF DICO- there are a few, in which they are entirely 



TYLEBONOUS SEED \ Cl, ' 



piumuia; 6, radicle; absent. The cotyledons, when exposed to 

 c,c, cotyledons, the light, become green, and perform for a 



time (though imperfectly) the functions of leaves ; at the same 



