174 



MECHANICAL SYSTEM 



position, by the intrusion of sub-epidermal parenchyma. The general 

 disposition of the mechanical strands nevertheless remains decidedly 

 peripheral. In contrast to the preceding systems, the success of which 

 depends more upon the advantageous arrangement of the mechanical 

 tissue than upon its massive development, the present system is chiefly 

 remarkable for the large size of the fibrous strands, which can thus 

 readily provide the requisite degree of inflexibility, provided they can 



Pig. 59. 



Mechanical system of the haulm of Juncus glaucus. A. T.S. of aerial portion of 

 haulm. B. T.S. of subterranean portion. ft T.S. 1"5 cm. below the apex of the 

 haulm ; at b the subepidermal fibrous strands have fused with the outer fibrous 

 sheaths of the subtending mestome-bundles. Development of a composite peripheral 

 I-girder from a common procambial strand ; 6, bast-procambium ; c, mestome- 

 procambium ; g, protoxylem vessel ; e, the portion of the procambial strand which 

 will give rise to parenchyma. 



find a place anywhere near the periphery. The haulms of Bamboos, 

 and the stems and inflorescence-axes of Palms, are cases in point. In 

 Palms the fibrous sheaths of the mestome-bundles frequently become 

 fused tangentially into an irregular ribbon-shaped strip : in this case 

 they collectively form a hollow cylinder (Fig. 60), with a wall which 

 is thin in comparison with the diameter of the whole organ. The 

 more deeply-seated mestome-bundles have relatively slight fibrous 

 sheaths, which serve solely for purposes of local protection, without 



