196 



PART II. THE INTIMATE STRUCTURE OF PLANTS. 



[35. 



principal product of the activity of the cambium, the cell-walls 

 are not lignified. J 



The secondary sclerenchyma consists of elongated pros- 

 enchymatous cells, with more or less thickened lignified 

 walls marked with narrow oblique bordered pits 

 (Fig. 94, p. 134; Fig. 148 A, B). Two forms 

 of this tissue are distinguishable : woody fibres 

 destitute of protoplasmic contents, which are 

 connected by transitional forms with the tracheids 



FIG. 148. Isolated constituents of the secondary wood of the Lime (Tilia 

 paroifolw,). A and B wood-fibres; C wood- parenchyma; D and E tracheids; 

 F segment of a wood- vessel (trachea). G is a bast-fibre. (x!80; after Stras- 

 burger.) 



(see p. 134) : fibrous cells, with protoplasmic cell-contents, 

 which are allied to the wood-parenchyma ; in fact, one 

 fibrous cell corresponds to a row of wood-parenchyma 

 cells ; the walls of the fibrous cells sometimes remain 

 thin, as in Viscum and some other plants, where they 

 replace the wood-parenchyma both structurally and func- 

 tionally. Both the woody fibres and the thick-walled fibrous cells 



