56 



BOTANY OF THE LIVING PLANT 



the strands, thus completing the cambial ring. The cambium then 

 forms a complete cylinder. The parts within the strands are called 

 fascicular, and those between them inter -fascicular cambium [i.e. 

 Fig. 25). In woody stems where the strands are closely grouped, 

 this distinction is not so obvious. 



Fig. 34. 



Transverse section of a single vascular strand from the young stem of the Elm. 

 «=endodermis. sc=sclerotic pericycle. st = sieve-tubes. cc = cambium. p.v.= 

 pitted vessels. £*=protoxylem. mr= medullary rays. P=pith. ( x 150.) 



The cambium is recognised by the repeated division of its thin- 

 walled cells by tangential walls, so that radial rows of cells are pro- 

 duced. As there is no limit to the repeated divisions, a great increase 

 of the tissues may be the result. The clearest evidence of division 

 is in the centre of each radial row, and it has been concluded from 

 careful comparison of many such rows that in each of them there is 

 an ultimate initial-cell, which retains its identity, giving off on the 

 one side cells formative of wood, and on the other cells formative 

 of bast. This has been styled SaniVs law of cambial division 



(Fig- 35). 



