92 PRACTICAL BOTANY 



root. The sections are of little use unless they are accurately 

 median. 



Treat the sections with potash for ten minutes or more ; or 

 better, treat with u eau de javelle " as directed on p. 32 : wash 

 with water, and mount in glycerine : examine with a low power, 

 and observe that 



1. The mass of tissue is composed of thin- walled cells, 

 arranged regularly in longitudinal rows. 



2. That these rows of cells converge towards a point at some 

 distance below the external apex of the root. This is the 

 centre of construction of the punctum vegetationis. 



3. Note also that the vascular cylinder of the root may be 

 traced upwards to the apex as the plerome cylinder, with a 

 dome-like ending. 



4. The cortex continues upwards as the periblem : it may 

 be distinguished by its darker appearance owing to the 

 intercellular spaces. 



5. The superficial piliferous layer, which curves inwards 

 under 



6. The tissue of the root-cap. 



The general scheme of arrangement of the apical meristem 

 of a root is indicated in the diagram, Fig. 1 1 : but in comparing 

 the sections with the diagram it must be remembered that the 

 figure represents an ideal Dicotyledonous type, and it must not 

 be attempted to trace a correspondence of minute detail of the 

 sections with the diagram : thus in the diagram there is a sharp 

 limit K K, between the root-cap and the body of the root, 

 whereas in the Sunflower, as will be presently shown, the root- 

 cap and piliferous layer have a common origin. 

 Examine with a high power : and observe that 

 I. At some distance from the apex a definite 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. Fol- 

 lowing 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 



