APEX OF ROOT 159 



piliferous layer covers the root externally. Follow this 

 towards the apex : at some short distance from it 

 this single layer splits into two : the inner is the 

 dermatogen, formative of the piliferous layer : the 

 outer is the outermost layer of the calyptra, or root- 

 cap. Following the dermatogen further inwards, it 

 will be seen to split again several times in succession : 

 the dermatogen may be traced as a continuous layer 

 covering the inner tissues. The 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 abroad band of formative tissue of the cortex, or 

 periblem : follow this to the punctum vegetationis : 

 it is also a distinct continuous band, though reduced 

 to a single layer of cells at the apex. 



3. The plerome, 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 : 



Calyptrogen ] a single layer of cells, i.e. piliferous layer 

 Dermatogen ) and root-cap have a common origin. 

 Periblem, distinct from the rest. 

 Plerome, distinct. 



To this type belong most of the Dicotyledons. The 

 work may be equally well done on Linum usitatissimum 

 or Polygonum Fagopyrum. 



Type II. Prepare median longitudinal sections of 

 the apex of the radicle of Phaseolus multiflorus (the 

 Scarlet-Runner), or perhaps better, from the Broad-Bean : 



