148 



MORPHOLOGY OF TISSUES. 



the part of the dermatogen which covers the apex of the root divides periodically 

 by tangential walls. Thus the dermatogen splits at the apex into two layers of cells, 

 the outermost of which developes into a many-celled cap, the Root-cap, while the 

 inner layer at first again performs the functions of dermatogen, until a new splitting of the 

 layer at the apex causes the formation of a new stratum, which again, on its part, as 



Fig. 114.- Longitudinal section through the apical region of the young root of the sunflower (after Reinke) ; A A the root- 

 cap ; b b (figured dark) the dermatogen ; // the plerome ; its inner (dark) layer ir tt the pericambium; between ir and b lies the 

 periblem ; i i the primary mother-cells, the source of the periblem and plerome. 



in Cryptogams, becomes separated by tangential divisions into several layers, as is 

 exemplified in Fig. 114. 



According to the description here given, which can only serve as an introduction to 

 what follows for the student in a few examples, it might almost appear as if the processes 

 in the growing point of Phanerogams were essentially different from those in Cryptogams, 

 a hypothesis which I however do not accept. On the one hand the careful investigations 

 of Nageli and Leitgeb in Lycopodiaceae (/. c.) on this point prove that in this family the 

 significance of the apical cell in the production of the primary meristem is different from 

 that in other Cryptogams, and approximates to what occurs in Phanerogams; and 

 that, on the other hand, the apical cell of Cryptogams may, equally with the apical cell- 

 , group of Phanerogams, be considered the starting-point of the first difFerentation of the 

 layers of tissue. 



