THIGKENINOH OF THE WALL. 



37 



away as in the previous case, and so free communication 

 between adjacent cells or vessels is established. 



Fig. 18. 



Fig. 17.— Bordered pits of the thick root of Dahlia variaUlls. A, front view of a 

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

 (horizontal, auu at right angles to the paper) ; C, loni-ituilinal section of A (vertical, 

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

 J, the expanded part of the th ckeinnj musses, formed later and overarching the pit ; 

 «, the fissure through which the cavity of the pit communicates with the cell cavity ; 

 at a and ^ the corresponding front view is appended, in order to make the trans- 

 Terse and longitudinal sertlona more clear. X 800.— After Sachs. 



Fig. 18.— Scalariform thickening of the walls of a vessel from the underground 

 stem of Pteris OQuilina. A, half-vessel, isolnted by Schulze's maceration ; ^ to JD, 

 pieces'obtained from stems hardened in al)solute alcohol ; B, a partly diagrammatic 

 view of a vertical section or 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 ; Vy thickening-ridge ; Z>, vertical section of C; E^ section of wall m a place 

 where a vessel adjoins a succulent cell p/ the thickening-ridges (ff) are only on 

 one side. X 800.— After Sachs. 



tionary," third edition, 1874; 

 tidn, 1874 



Carpenter's "The Microscope," fifth edi- 



