GENERAL CONCLUSIONS 



177 



successively at right angles (A), planation leads to a system 

 of dichotomies in one plane (B). Overtopping is the result 

 of unequal dichotomies, and tends to produce a main axis 

 with lateral branches (C) ; the culmination of this process is 



Fig. 28 



The Telome Theory: 1, planation; 2, overtopping; 3, syngenesis; 

 4, reduction; 5, re-curving, h-k, evolution in Sphenopsida; 

 L-o, evolution in Pteropsida; p-s, evolution in Lycopsida. The 

 Enation Theory : t-v, evolution of microphylls in Lycopsida 



(a-s, after Zimmermann; t-v, Bower) 



a monopodial system. Syngenesis results from the coales- 

 cence of apical meristems. When they fuse to form a 

 marginal meristem ('foliar syngenesis'), a lamina with veins 

 develops (D) and the process is called 'webbing'. Zimmer- 

 mann also visuahzes a second type of syngenesis ('axial 

 syngenesis') in which several branches become absorbed 

 into a single stout axis with a complex stelar anatomy (not 



