X34 THE STRUCTURE OF ECONOMIC PLANTS 



The young stem is more or less grooved and ridged, owing to 

 the development of the principal bundles and the longitudinal 

 strands of collenchyma. (Fig. 113.) These are arranged in a ring 



. — coll V , — Iv 



/-■u ep 



■ r~hP-cot 



/--ep hr 



r-Ph ) 

 I — mx > mv 



Fig. III. Transection of cotyledons near their bases and enclosed apex of shoot: coll v 

 collar vein; cot, cotyledon; ep hr, epidermal hair; / i-/ i', first pair of foliage leaves; / z- 

 / i', second pair ; / 3-/ 3', third pair ; / ep, lower epidermis ; Iv, lateral vein ; mv, mid vein ; 

 mx, metaxylem ; ph, phloem; px, protoxylem ; s, stem tip; st, stoma; u ep, upper epi- 

 dermis. (After Berkman.) 



and are separated from one another by medullary rays which are 

 later occluded when an interfascicular cambium develops and 

 secondary thickening is begun. 



The epidermis is somewhat cutinized, producing numerous hairs 

 and glands. The pointed non-glandular hairs are unicellular and 



