THICKENINGS OF THE WALL. 



away as in the previous case, and so free communication 

 between adjacent cells or vessels is established. 



B 



FIG. 18. 



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

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

 (horizontal, and at right angles to the paper) ; C, longitudinal section of A (vertical, 

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

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

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

 at 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. Scalariform thickening of the walls of a vessel from the underground 

 stem of Pteris aquilina. A, half-vessel, i soli ted by Schulze's maceration ; to D, 

 pieces obtained from stemn hardened in absolute alcohol ; S, a partly diagrammatic 

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

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

 wall; v, thickening-ridge; Z>, vertical section of C; ^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, t874. 



