ZEA MAYS 



119 



zone. The bulliform zone is a band of epidermal cells two to five 

 or six rows in width which consists of motor cells, basal cells, and 

 the trichomes arising from the latter. The bulliform cells are 

 approximately hexagonal, protruding slightly above the surface of 

 the leaf, and extending deeper in the mesophyll than do the other 

 epidermal cells. The trichome, which arises from the center of a 

 group of basal cells, is a single thick-walled cell with a neck-like 

 constriction where it passes through the basal cells. 



The zone of narrow epidermal cells is limited to those portions 

 of the surface which overlie the vascular bundles; and varies in 

 width depending upon the size of the bundle. The cells are narrow 



ac c 



I sp 



Fig. 51. Transection of a portion of the leaf : ^cc, accessory cell ; ^«, bundle; e/^, epidermis ; 

 g c, guard cell ; i sp, intercellular space ; m c, motor cell ; ph, phloem ; scl, sclerenchyma ; 

 sto, stoma; xy, xylem. (After Avery.) 



w^ith sinuous margins and may lie end to end in a series. Fre- 

 quently, they are separated from one another by short cells of two 

 kinds — silicified cells and crescent-shaped cells, the latter usually 

 occurring in pairs or in a series of pairs. The silicified cell is two- 

 to four-lobed and may contain crystalline inclusions. The cres- 

 cent-shaped cells are roughly semilunar, three to five times as wide 

 as long, with walls that are somewhat thinner than those of the 

 adjacent epidermal cells. 



The stomatal zone ranges from three to fourteen cells in width 

 and contains epidermal cells with very undulate walls. They may 

 be joined end to end in series; but, more commonly, are separated 

 from one another by two-celled hairs, crescent-shaped cells, silici- 

 fied cells, horn cells, or the stomatal cells. The two-celled hair is 

 probably a modification of the crescent-shaped cell and is thin- 

 walled with dense cytoplasm. The horn cells are usually confined 

 to the border of the bulliform zone and are fairly thick-walled, 

 frequently being associated with silicified and crescent-shaped 



