478 THE STRUCTURE OF ECONOMIC PLANTS 



The bundle cap subtending the outer, abaxial face of the phloem 

 is composed of enlarged parenchymatous cells whose walls have 



Fig. 2.45. Details of phloem structure : A, B, two transections of a sieve tube with sieve 

 plate in A; C-G, stages of sieve tube differentiation shown in longisection ; H-M, stages of 

 phloem development shown in transection: cc, companion cell; obi, obliterated tissue; 

 0^, oil duct; J/, sieve tube ; f, vessel. (^Aker Esa.u, Htlgardia.^ 



