43' 



THE STRUCTURE OF ECONOMIC PLANTS 



— gl hr 



leaves, floral parts, and in the pericyclic and secondary ray tissues 

 of the stem. Stanford and Viehoever (33) have investigated them, 

 as well as the nectaries, and state that the former are lysigenous in 

 their development, although some of them may be formed by the 



enlargement of a single 

 cell. With respect to their 

 contents, they report that 



"The glands in portions 

 of the plant which are 

 exposed to light are sur- 

 rounded by an anthocyan- 

 bearing envelope of flat- 

 tened cells, and contain 

 quercitin, . . . ethereal oil, 

 resins, and perhaps tan- 

 nins. The glands not nor- 

 mally exposed to the light 

 are surrounded by a layer 

 of flattened cells contain- 

 ing no anthocyans; they 

 contain gossypol." 



-y:^ CO par 



The epidermis consists 



of a single layer of com- 

 pact cells which are uni- 

 form in size and shape with 

 thick outer walls overlaid 

 by a cuticle. There are 

 numerous stomata, each 

 bounded by two small 

 guard cells, which are 

 raised slightly above the 



Fig. 12.1. Transection of portion of young stem: SUtface of the epidermal 

 ca, cambium; col, collenchyma; co par, cortical pa- ]^ygj. TwO tVpCS of epi- 

 dermal hairs are produced, 

 one of which is long, 

 slightly pointed, unicellu- 

 lar and subtended by a group of basal cells. The other is smaller, 

 capitate, multicellular, and usually consists of a stalk of three cells, 

 the outer, broadly wedge-shaped one bearing a terminal group of 

 four cells that are probably glandular. As maturation of the 

 stem proceeds, the epidermal and cortical regions become fissured. 



renchyma; cu, cuticle; ep, epidermis; gl, gland; gl hr, 

 glandular hair; hr, hair; mx, metaxylem; ph i, pri- 

 mary phloem; ph z, secondary phloem; pi, pith; px, 

 protoxylem; ra, medullary ray; xy z, secondary xylem. 



