418 



XXX. THE SEED OF ANGIOSPEKMS. 



Take first of all cross-sections of the grain at about mid-height, 

 and examine them in water or in glycerine, and subsequently with 

 the addition of a little potash. Leaving the somewhat complex 

 structure of the furrow out of the question for the present, we find 

 that the pericarp is composed externally of one or several layers 

 of thickened pitted cells, the walls of which are highly refractive 

 and yellowish, and colour a deep yellow in potash. The outer - 



VJ* 



ce 



FlG. 151. Grain of Triticum vulgare, the wheat. .1, cross -section through the peri- 

 carp and testa. Of these, ep is the epicarp (epidermis) ; e, outer layers of the 

 mesocarp ; and chl, chlorophyll layer ; these collectively constituting the pericarp ; 

 ii, remnants of the ovular integument ; n, the outermost thickened layer of the 

 nucellus ; these together constituting the testa ; al, the aleuroue layer of the 

 endosperm (x 240). B, median longitudinal section through the lower part of a ripe 

 fruit. At the bottom of this, to the left, is the embryo with the scutellum, sc ; 

 I', the tooth-like development of the scutellum ; vs, its vascular bundle ; ce, its 

 "cylinder epithelium " ; c, the sheath of the cotyledon ; pv, the growing apex of the 

 stem ; hp, the hypocotyl ; I, the epiblast upon it ; >-, the radicle ; cp, the root-cap of 

 the radicle ; cl, the root-sheath (coleorhiza) ; m, place of exit of the radicle, corres- 

 ponding with the micropyle of the ovule ; p, the funicle ; vp, vascular bundle in the 

 funicle ; /, side wall of the furrow (*x 14). 



most layer of these cells is the epidermis (Fig. 151, A, ep), the 

 succeeding layers (e) belong to the inner tissue of the pericarp, the 

 innermost layers of which are for the most part obliterated. To 

 this outer tissue succeeds a layer of tangentially-elongated, 

 straight, or more or less curved, cells (chl), marked by numerous 

 narrow, cross-set pits. Now and again on the inner side of this 

 pitted layer we see sac-like cells, which indicate the inner epider- 



