THICKWmNQS OF THE WALL. 



27 



away as in the previous case, and so free commnnication 

 between adjacent cells or vessels is established. 



Fig. 18. 



Pig. 17.— Bordered pits of the thict root of DaMia variabilis. A, front view of a 

 piece of the wall of a vessel, seen from without ; B, transverse section of the same 

 (h'Tizontal, and at right angles to the p;iper) ; C, lont^itudinal section of A (vertical, 

 and at right angles to the paper) ; q, septum ; a, the orif;iual thin thickening- ridge ; 

 6, the expanded part of the thekenm^; masses, formed later and overarching the pit ; 

 c, the fis-*ure through which the cavity of the pit communicates with the ceil cavity ; 

 at d and 3 the corresponding front view is appended, in order to make the trans- 

 verse.and longitudinal sections more clear. X 800.— After Sachs. 



Fig. 18.— Scalariforra thickening of the walls of a ve-sel from the underground 

 stem of Pteris aquHina. 4., half-ves«el, isol ited by Schulze's macerfitlon ; B to D^ 

 pieces obtained from stemn harde ed in absolute alcohol ; B, a partly diagrammatic 

 view of a vertical section of the wall, seen from within ; c, c, plan of section ; d. 

 opening to pit ; C\ front view of young wall of a vessel ; s, unthickened portion of 

 wall; V, thickenin§;-ridge ; i>, vettical section, of C; E^ section of wall in a place 

 where a vessel adjoins a succulent cell p; the thickening-ridges {g) are only on 

 one side. X 800.— After Sachs. 



tionary," third edition, 1874; Carpenter's "The Microscope," fifth edi- 

 tion, 1874 



