CANNABIS SATIVA 



12-9 



In the ontogeny of the root, the primary structures are derived 

 from three well-defined histogens which are similar to those 

 described by Janczewski (i6) and Crooks (9) for the primary root 

 of Linum usitatissimum. The root cap and epidermis are derived 

 from a common layer of initials designated as the calyptrogen- 

 dermatogen. The cortical tissue originates from the two-layered 

 periblem, and the stelar tissues are derived from the plerome. 



The development of the root cap and epidermis from the calyptro- 

 gen-dermatogen layer results from the differential character of the 



B 



Fig. 1 10. A, transection of primary root 0.6 mm. above root tip; B, median longisection 

 of root apex showing histogens in detail : cal, calyptrogen ; co, cortex ; dgn, dermatogen ; 

 en, endodermis; ep, epidermis; hd, hypodermis; mx, metaxylem; pbm, periblem; pel, 

 pericycle; ph, phloem; />/, plerome; />x, protoxylem ; >-c, root cap. (After Berk man.) 



division of its cells. The cells of this layer which immediately 

 overlie the periblem at the tip of the root divide periclinally to 

 form the root cap cells. The more laterally placed ones divide 

 anticlinally, and function as a true dermatogen in producing the 

 epidermis. The manner in which the root cap and dermatogen 

 arise from the dual histogen has been described by de Bary (i): 



"The divisions of the initial layer, which are parallel to the surface 

 of the bluntly conical apex, add on the one hand new cells to the root- 

 cap above the apex, and on the other hand renew the initial layer 

 itself. As the distance increases from the apex of the periblem, which 

 by its growth in length is constantly advancing, the divisions become 

 rarer, and at last cease. The last of these separates the initial cell 



