196 



PART II. THE INTIMATE STRUCTURE OF PLANTS. 



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

 are not lignified. i 



The secondary sclerenchyma consists of elongated pros- . I 

 enchymatoTis ceils, 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 secondly wood of the Lime (Tii,ii 

 pamifolia). A and B wood-fibres; C wood -parenchyma ; Dnnd E tracheids; 

 P Segment of a wood-vessel (trachea). G is a bast-fibre. ( x 180; after Stras- 

 burger.) 



(see p. 134) : fibrous ce/Zs, 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 



