SECONDARY XYLEM 



663 



111 



,' : X>. : 





000*1 

 ..eP ov; 



QD 



D 



L 



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( i 



'v 



s 



rih 



Fig. 275. 



Various constituents of the secondary wood of Ci/tisus Laburnum (taken from a 

 tangential L.S.). A. Intermediate cell, containing starch. B. Ends of two adjoining 

 xylem-parenchyma cells, ft A transitional element which has the characters of a 

 wood-fibre at its lower end, and those of an intermediate cell at its upper extremity. 

 D. Two water-conducting elements; on the left a tracheide, on the right a narrow 

 vessel; e, the perforations in the transverse septa of the vessels. B. Small portion 

 nf the wall separating two tracheides, showing bordered pits and spiral thickening 

 fibres. 



ducting and storing elements of the wood : such transitional forms in 

 many cases actually make up the bulk of the woody cylinder, which 

 thus acquires a very characteristic histological composition. 



To begin with, we may consider the series of intermediate forms 



