APICAL CELL OF PTERIS. 



225 



study the root of Pteris cretica (Fig. 89), but can equally well 

 choose any other species of Fern. By turning upside down a 

 flower-pot in which the fern is growing we easily obtain un- 

 injured root-apices. The roots of Pteris cretica, as of ferns 

 generally, are diarch ; with the xylem portions alternate flat- 

 tened strands of bast ; the pericycle is unilamellar, the endoder- 

 mis flattened, the primary cortex has become brown, and in its 



FIG. 89. Median longitudinal section through the root of Pteris cretica. t, apical 

 cell ; k, initial cell of root-cap ; &, outermost layer of root-cap ; c, median cortical 

 wall ; p, outer wall of the central cylinder ; r, inner cortical wall ; e, epidermal wall 

 (x 240). 



inner part strongly thickened. We now 7 endeavour to obtain, 

 between thumb and forefinger, a thin, median longitudinal 

 section of the root-apex. It is not very difficult to bring into 

 view the apical cell, which is covered by the tissue of the root- 

 cap. This apical cell (t, Fig. 89) has, as in the stem of Equisetum, 

 the form of a three- sided pyramid, whose convex base is turned 

 towards the cap, while the apex, formed by the junction of the 



15 



