5o6 THE STRUCTURE OF ECONOMIC PLANTS 



arranged in a disk to form the flattened or convex surface of the 



scale. 



The Anatomy of the Young Stem. — The epidermis of the 

 young stem is thin-walled and produces numerous glandular scales 

 and non-glandular hairs. The scale has a flat basal cell which 

 arises from a small somewhat sunken epidermal cell so that the 

 terminal portion of the scale appears to rest in a saucer-like depres- 

 sion in the epidermal surface. (Fig. 2.66, A.^ The distal part is 

 composed of several cells which are formed by vertical divisions of 



Fig. 165 . Transection of portion of lamina of cotyledon through midvein : col, collen- 

 chyma; wa:, metaxylem ; o /)/>, outer phloem ; /?<«/, palisade; /?a:, protoxylem. 



the terminal cell of the scale. The non-glandular hair has a basal 

 stalk cell which arises from an epidermal cell or a group of epider- 

 mal cells and a tubular terminal portion which is divided trans- 

 versely into two or more cells. (Fig. 1.66, B.) These hairs may 

 or may not persist on the mature stem, and their frequency appears 

 to be a varietal character. The stoma is somewhat raised above 

 the adjacent epidermal cells, due in part to the position of 

 the two accessory cells which lie parallel to the guard cells. (Fig. 

 i66,C.) 



The cortical chlorenchyma is compact and there are numerous 

 vertical latex canals, usually bounded by four to six secreting cells, 

 located centrad to the two hypodermal layers. Crystals of calcium 



