EPIDERMIS. 



97 



covered by the closely applied cuticle. Their outer ends are prolonged, so that they 

 form a radiating ring round the margin of the flat surface. The cells, about 25 in 



Fig. 41. — a, b Rhododendron ferrugineum ; glandular scales of the under surface of the leaf, a surface view of a larger one ; 

 * transverse section of a smaller one (142). In the latter the cells are shaded ; the intervening spaces filled with secretion, not 

 shaded.— 1: Rhododendron hirsutum ; glandular scales from the under surface of the leaf, transverse section (225). The cellulose 

 membrane of the scale dotted, cell-contents and secretory space left white ; over the cellulose membrane runs the cuticle, which 

 is connected with that of the surrounding epidermis. In all cases the secretion has been removed by alcohol. 



number, which form the central part of the scale, are much reduced between their two 

 ends, and the wide interstices thus formed between their lateral cellulose walls (which 

 turn deep blue with Schultze's solution) 



are filled with the secretory mixture — 

 resin and ethereal oil. 



The almost globular head of the above- 

 named larger glandular hairs of the leaf 

 of Ledum consists of 9-10 cells which 

 diverge from the end of the stalk. The 

 polygonal outer ends of these are distri- 

 buted over the periphery of the sphere, 

 remaining in immediate lateral connec- 

 tion with one another, and adhering 

 closely to the cuticle. The cellulose 

 walls become suddenly reduced inwards 

 to narrow tubes, which meet at the stalk, 

 and leave between their sides a wide 

 space, which is also filled with a resinous 

 secretion. 



The manner in which these cavities 

 filled with resin arise may be most clearly 

 observed in the imbedded intra- mural 

 glands of Psoralea (Fig. 42). At each 

 of the clear spots on both leaf-surfaces 

 of the above quoted species lies an al- 

 most spherical body, which protrudes 

 into the tissue of the leaf: its outer flat- 

 tened pole often lies in a slight depres- 

 sion or excrescence of the outer surface 

 of the epidermis. In the superficial 

 view of the epidermis it shows the poly- 

 gonal outer walls of a group of about 

 20-30 cells (the number varies according 

 to the individual), these outer walls 

 being much smaller than those of the 

 surrounding epidermal cells, but at least 



Fig. 42. — Transverse section of the lamina of Psoralea hirta ; one- 

 layered epidermis, and the tissue beneath it ; the latter in b and c 

 distinguished from the epidermis by the shading ; a (375) an almost 

 mature gland after removal of the secretion by alcohol ; b (600) a very 

 young stage of a gland, secretion not yet present ; c (600) rather 

 older, development of secretion beginning. 



H 



