d 



per 



SPERMATOPHYTA 



365 



per 



Fig. 310. Median longitudinal section of a root tip of onion {Allium cepa), showing 

 histogens, X 170; d, dermatogen; per, periblem; pl, plerome; re, rootcap. At the tip of the 

 plerome is a layer of cells that gives rise to the periblem and dermatogen. Below this 

 layer is the calyptrogen, which produces the rootcap. 



