Meristems 



61 



Fig. 4-6. Diagram of shoot apex according to Hanstein's interpretation. D, dermatogen; 

 Pe, periblem; PI, plerome. (After Buvat.) 



if it could be supported. There is now much evidence, however, that no 

 constant relation exists, valid for all plants, between these "histogens" 

 and the structures formed by them. Some of this evidence comes from 

 direct observation, as in Schoute's (1902) studies on the origin of the 

 vascular cylinder. Some is derived from the structure of periclinal chi- 

 meras (p. 268) in which the layer or layers derived from one graft com- 

 ponent can be distinguished by the size of their cells from those coming 

 from the other, a distinction that persists in the mature structures and is a 



Fig. 4-7. Vinca minor. Longitudinal section through shoot apex, showing three-layered 

 tunica and unlayered corpus beneath it. ( From Schmidt. ) 



