THE VASCULAR TISSUES. 



67 



although more rarely than the other above-mentioned elements. 

 They are formed by the junction end to end of several tracheides, 

 and they have thick walls in which occur slit-like pits surrounded 

 by a narrow thickened border (see Fig. 46). 



(g) Lying amongst the other elements a few cells occur in 

 some stems, which are termed wood-parenchyma- Each cell is 

 thick-walled, with simple pits in the walls, and internally are to 



jy^ 



Fig. 49.— Tracheides seen in Teansvbese 

 Section. — xyi, Young tracheides ; xy^, older 

 elements. 



Fig. 48. —Bordered - PITS 

 (r)) IN Tangential Sec- 

 tion.— The middle lamella 

 is seen in section, and the 

 torus appears as a central 

 thickening on this ; m, 

 medullary ray. 



Fig. 50. — Portion of a Teacheide showing 



BOKDERBD-PITS IN COURSE OF FORMATION 

 (Pinu^). 



