32 



MORPHOLOGY OF THE ANGIOSPERMS 



position in the plant, vigor of the shoot, and season. To improve in- 

 terpretations, it was suggested that the terms tunica and corpus be 

 replaced by mantle and core — so defined as to avoid the rigidity of the 

 earlier use and to allow considerable variation in some characters. 

 Mantle is defined as consisting of all the distinct peripheral layers of 

 the apex in which anticlinal cell divisions maintain the layers. The core 



B 



Fig. 11. Diagrams to illustrate two concepts of growth in dicotyledonous shool 

 apex. A, the tunica corpus theory: zone 1 and 1', initials of tunica layers; zone 2, 

 corpus initials; zone 3, peripheral zone; zone 4, rib meristem. B, the mantle-core 

 concept: zone 1, mantle layers; zone 2, central-mother-cell zone; zone 3, cambium- 

 like zone; zone 4, rib meristem; zone 5, peripheral zone. {After Gifford.) 



