MORPHOLOGY OF HIGHER PLANTS. 429 



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

 are usually thickened, in hyoscyamus (Fig. 251), 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 

 and flaxseed (Fig. 119) ; or to non-glandular hairs which consist 

 either of cellulose, as in cotton (Fig. 139), or lignocellulose, as 

 in nux vomica (Fig. 119). 



The PERispERM and endosperm (Fig. 249) consist chiefly of 

 parenchyma cells, which contain, besides protoplasm, starch, as 



A B ^ 



Fig. 251. Seeds: A, of Hyoscyamus muticus with epidermal cells having wavy, thick- 

 ened walls, those at the edge are seen in section and showing that the outer wall is not 

 thickened. B, of Lobelia infiata showing reticulate seed-coat composed of uniformly thick- 

 ened and strongly lignified cells. C, of Apocynum cannabinum with numerous long i-celled 

 hyaline hairs. 



in physostigma ; oil, as in flaxseed and cottonseed ; aleurone grains, 

 as in ricinus (Fig. 250); glucosides, as in almond; alkaloids, 

 as in stramonium. The walls are usually thin, but may in some 

 instances be considerably thickened, as in coft'ee, colchicum, and 

 nux vomica (Fig. 135). 



The embryo consists chiefly of parenchyma cells with a few 

 fibrovascular bundles: the cotyledons may be thin and leaf-like, 

 as in ricinus and nux vomica, or thick and fleshy, as in almond 

 and cola, or partly developed, as in strophanthus ; the hypocotyl 

 is usually small, but in the Umbelliferae it is as large as the 

 cotyledons. 



