THE PHYSIOLOGY OF PLANTS 



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i. 13.— Transverse Section through the 

 Wood and Bast of a One-Year Old Shoot 

 OP Cytisus Laburmiin, out AT the end of 

 May in the Second Year (after Luerssen). 



parenchymatous cortex ; b, bast fibres ; st, 

 schlereuchymatous cells ; bp, bast paren- 

 chyma ; c, cambium ; g, wood vessels ; h, 

 wood cells (libriform) ; t, tracheids ; hp, wood 

 parenchyma ; g, vessels ; m, medullary ray. 



of thick-walled hard - bast 

 cells, h, and other groups of 

 hard cells, st (selepenehyma). 

 The cells have the shape of 

 parenchymatous cells, but 

 have excessively thick walls, 

 penetrated by canals or pits, 

 and are very like bast 

 fibres. 



The woody cylinder can 

 be divided into the firm 

 wood of the previous year 

 (ah), and the not quite so 

 thick-walled wood of this 

 year (nh) which has been 

 formed up to the month of 

 May, The elements which 

 make up the old wood and 

 the new wood are the same. 

 We recognise the large open 

 vessels (g) lying between 

 the wood fibres (h), with 

 their small lumen. These 

 masses of wood are radially 

 divided up by the lignified 

 parenchyma, which makes 

 up the medullary rays (m). 



Fig. 1 4 represents a lon- 

 gitudinal section through the 

 same piece of twig. 



Here we recognise that 

 the cambium layer (c) is 

 built up of thin- walled cells 

 with blunt ends, and which 

 in their transition to bast 

 cells {hj}) still retain their 

 original shape and size, but 

 have become slightly broader 

 and thicker-walled. On the 

 other side, however, towards 



