2IO 



BOTANY AND PHARMACOGNOSY. 



may be covered or whitened with a bloom, as in magnolia, when 

 the leaves are spoken of as glaucous. 



In other cases the outer walls of the epidermal cells are modi- 

 fied to hairs (Figs. 283-285). When the hairs are unicellular 

 and lie over one another in one direction, they give the leaf a 

 SERICEOUS or silky appearance ; when they are very short and 

 straight, the surface is described as puberulent ; or when they 

 are still longer, as pubescent; or when long and straight, as 



Fig. 117. Transverse section of midrib of leaf of stramonium: EU, upper epidermis; 

 CO, collenchyma; PA, palisade cells; O, layer of cells containing rosette aggregates of 

 calcium oxalate; M, loose mesophyll; EL, lower epidermis; OP, prisms of calcium oxalate; 

 OS, cryptocrystalline crystals of calcium oxalate; ST, stoma; T, ducts; SU, sieve on upper 

 side of ducts; SL, sieve on lower side of ducts, this arrangement of sieve and ducts forming 

 bicollateral fibrovascular bundles. 



PILOSE ; when the hairs are long and matted together, as tomen- 

 TOSE, or woolly; when they are hard and prickle-like, the leaf is 

 spoken of as hispid, or strigose; when modified to spines, as 

 spiNOSE, and when they are hooked as echinate. 



In still other cases the epidermal cells are uneven, forming 

 depressions and protuberances which, if slight, the surface is de- 

 scribed as rugose; or if wart-like, as varicose. Furthermore, 

 the veins may be quite prominent, particularly on the lower sur- 



