APEX OF ROOT 



93 



layers thus thrown off externally from the dermatogen form 

 collectively the root-cap, or calyptra. We have in this case 

 a common formative layer for root-cap and piliferous layer. 



2. Between the procambium and the piliferous layer lies 

 a broad band of formative tissue of the cortex, or periblem :' 

 follow this to the punctttm vegetationis : it is also a distinct 

 continuous band, though reduced to a single layer of cells at 

 the apex. 



K 



p IG g. Diagram illustrating the arrangement of a meristem which may be found 

 at the apex of a root of a Dicotyledon, h h h, the root-cap, limited internally 

 by the line K K K, which represents the outer limiting wall of the dermatogen. 

 In the root-cap the letters A A indicate anticlinals ; P p, the periclinal curves. 

 (After Sachs.) 



3. The pierome, or central procambium cylinder, may also 

 be traced as distinct up to the apical point. 



This type of arrangement of tissues of the meristem may then 

 be expressed thus : 



fCalyptrogen \ a single layer of cells, i.e. piliferous layer and 

 I Dermatogen / root-cap have a common origin. 

 | Periblem, distinct from the rest. 

 vPlerome, distinct. 



