52 LEAVES. 



(30) Bearberry Leaves. 



The leaves of Arctostapliylos Uva-ursi, Sprengel (N.O. Ericaceae). 



The upper epidermis is composed of polygonal cells with 

 slightly wavy walls, covered by a thick cuticle ; they measure from 

 25 to 40/i either in length or width. The lower epidermis 

 is furnished with very large stomata, surrounded by four, five, 

 or six cells, which, however, are devoid of any regularity in 

 their arrangement. Both short simple hairs and glandular 

 hairs are occasionally to be found, but they are often rare. The 

 former are one-celled and conical ; the latter have a short two- 

 celled pedicel upon which a large pluricellular oval gland is 

 borne ; the gland is divided by horizontal and vertical walls into 

 several cells. 



The mesophyll is heterogeneous, asymmetrical and destitute 

 of internal glands. The midrib is plano-convex. The wood is 

 fan-shaped, strongly curved below, but only slightly above; the 

 bast passes gradually into a cortical tissue composed of more 

 or less distinctly axially elongated collenchymatous cells. Both 

 in this tissue and in the bast there are superposed rows of small 

 cells, or axially elongated cells containing crystals of calcium 

 oxalate; these may be prismatic or cluster crystals, both forms 

 being frequently found in the same (elongated) cell. 



The diagnostic characters of powdered bearberry leaves are : 



(a) The lower epidermis with very large stomata. 



(b) The crystal cells of the cortical tissue. 



