iMORPHOLOGY OF HIGHER PLANTS. 217 



an inner epidermis of more or less obliterated and elongated 

 cells, between which is a thin-walled parenchyma traversed by a 

 number of fibrovascular bundles (See also Figs. 246, 250, 252). 



In some cases the outer epidermis contains numerous sto- 

 mata, as in poppy capsules, or is developed into hairs and other 

 outgrowths or appendages, as in anise (Fig. 244 j, arnica, rhus 

 glabra and raspberry. 



The inner epidermis may also contain stomata, as in the poppv, 

 or be developed into hairs, as in vanilla (Fig. 256) and orange, 

 or more or less obliterated, as in akene-like fruits, or modified to 

 sclerenchymatous elements, as in drupes. 



The middle la}'er, which is composed of parenchyma, may con- 

 tain protoplasm, starch, sugars, calcium oxalate, coloring princi- 

 ples, alkaloids and other principles, and it may also have oil-secre- 

 tion cells, as in cubeb (Fig. 250) or oil-secretion canals, as in 

 orange and the fruits of the Umbelliferae, in the latter of which 

 they arc known as vitt?e (Figs. 244 to 248) ; milk vessels some- 

 times occur, as in poppy ; a collenchymatous layer is sometimes 

 developed beneath the epidermis, as in capsicum (Fig. 252), in 

 some cases sclerenchymatous cells may be present, as in pimenta 

 and cubeb (Fig. 250) ; and in still other instances the entire peri- 

 carp may be made up of stone cells. 



INNER MORPHOLOGY OF THE SEED. 



The SEED-COAT usually consists of from two to six layers of 

 cells: (i) an outer layer or so-called epidermis, (2) a layer of 

 sclerenchymatous cells or stone cells, (3) a pigment layer, (4, 5) 

 one or two rows of parenchymatous cells. (6) a row of more or 

 less obliterated parenchyma cells. 



The EPiDERAiAL CELLS vary considerably in different species, 

 both as regards the form of the cells and the composition of the 

 walls (Fig. 302). The cells may be more or less isodiametric in 

 cross-section, as in cardamom (Fig. 253) ; elliptical, as in almond 

 (Fig. 302, D) ; palisade-like, as in Ahnis precatoriiis, or more or 

 less irregular, as in Delphinium. While the outer and side walls 

 are usually thickened, in hyoscyamus (Fig. 302, A) it is the inner 

 and side walls which are thickened, the outer wall remaining thin. 

 The outer wall may be in part modified to mucilage, as in mustard 



