58 



BOTANY OF THE LIVING PLANT 



outside the ring. If this process be continued, the structure of the 

 stem will become like that shown in Fig. 2>7, C- 



2 



Fig. 37. 



Diagrams of secondary thickening in stem of Dicotyledon, based on transverse 

 sections of the hypocotyl of Ricinus. A represents the stem before origin of inter- 

 fascicular cambium. B, same after it has been formed. C, after it has produced 

 internally a broad ring of secondary wood, and externally a narrower ring of secon- 

 dary phloem. 2? = primary cortex. M=pith. £=phloem. #=primary xylem. 

 6 = bast fibres at periphery of phloem, fc = fascicular cambium. ic = interfascicular 

 cambium, fh = wood of primary bundle. i/fe = wood developed from inter- 

 fascicular cambium. ifp = phloem developed from interfascicular cambium. By 

 the intercalation of the secondary tissues the primary bast, b, b, b, is removed some 

 distance from the primary wood x, x. In C the principal medullary rays extend the 

 whole distance through the ring, the secondary rays only part of that distance. 

 (After Sachs.) 



Three different results accrue from the growth of the vascular 

 column, viz. increased power of conduction, of storage, and of mechanical 

 resistance. Three different types of tissue are involved, and though 

 differing in detail, all of these are to be found as a rule both in the 

 internal woody column and in the external band of bast. The 

 tissues in question are, the vessel for conduction, the parenchymatous 



