PRINCIPAL GROUPS OF PLANTS. 



127 



tion which is connected with the suspensor (Fig. 84, w) ; (2) one 

 or two cotyledons (Fig. 84, c) which are attached to the stem ; (3) 

 a little bud at the apex of the stem which is known as the plumule. 

 While the embryo is developing, the nucleus of the embryo- 

 sac, either after fusing with the prothallial cell of the pollen grain, 

 or in the absence of such union, begins active division, forming, 



FIG. 83. Diagrammatic representation of fertilization in an Angiosperm. d, floral leaves; 

 stamen consisting of filament (c) and anthers (a,b), one of which (b) has dehisced, exhibiting 

 numerous pollen grains; e, nectar-secreting bodies; pistil consisting of ovary (f), style (g), 

 and stigma (h). On the latter pollen grains (i) are germinating, the tube (1) of one of them 

 has penetrated the tissues of the stigma and style, and entered the foramen (m), or opening 

 of the ovule. The ovule consists of several parts: raphe (n), outer integument (p), inner 

 integument (q), chalaza (o), nucellus (s), embryo-sac or megaspore (t) with egg-cell (z), 

 synergids (v), antipodal cells (u), and the nucleus in the center which gives rise to the 

 endosperm. After Sachs. 



a highly nutritive tissue rich in starch, oil, or proteins, known as 

 the endosperm (see chapter on Seed). Simultaneously with the 

 development of the endosperm the nucellus may give rise to a 

 nutritive layer called the perisperm, or the tissues of the nucellus 

 may be modified and form, with the altered integuments or coats 

 of the ovule, the seed-coat. 



Inasmuch as the Angiosperms furnish by far the larger pro- 

 portion of plants and plant products used in medicine, it is desir- 



