20 



GROWING POINTS 



At the growing apex of the root four meristematic layers are 

 often distinguishable. Three, the dermatogen, periblem, and 

 plerome, serve the same purpose as in the stem ; but external to 

 the dermatogen is a fourth layer, the calyptrogen, which cuts off 

 segments towards the outside only, and thus gives rise to the 



Fig. 9. — Koot-tip of the Hyacinlli [SciUa] in longiludinal section showing 

 the growing point and the root-cap. Sonic of the nuclei (blacl-;) 

 cxliibit piliases in nuclear division (cf. p. 12). 



root-cap (Fig. q). The latter is constantly replenished liy the 

 growing point, as the older cells in front become disorganised. 

 In manj/ roots, however, the epidermis and root-cap arise from 

 a common rncristematic layer, and there are other modifications 

 of the growing point of the root \\hich it is nnnecessar}' to describe 

 in detail. 



