358 THE STRUCTURE OF ECONOMIC PLANTS 



cambium, and small groups of secondary xylem and phloem are 

 formed between the major bundles of the stele. The large, thin- 

 walled parenchymatous cells of the pith centrad to the connective 



^ sto 



€\Xy--<^\SQ(^^ chlpar 



^^^>--^;^3-£'~T^^> en 



pclfijj 



par 



p/i2 



Tj(jvWtr\HD<^^=w^^ TCI 



Fig. i8o. Transection of sector of upper internode showing vascular bundle : w, cambium; 

 chl par, chlorophyll parenchyma; col, collenchyma ; con, connective tissue of pith; cu, cu- 

 ticle; e«, endodermis ; ^/7, epidermis ; /»«r, parenchyma of pericycle ; /)c/ /^, pericyclic fibers ; 

 fh -L, secondary phloem ; ft, pith ; ra, ray ; sto, stoma ; xy i, primary xylem ; xy x, secondary 

 xylem. 



tissue usually disintegrate so that the mature stem is commonly 

 hollow. 



Anatomy of the Leaf — the Blade. — The blades of the paired 

 leaflets are very thin, and the mesophyll, except in the region of 



