200 RELATION OF PHYLLOTAXIS TO MECHANICAL LAWS. 



types, and are evidently due to a change in the bulk-ratio of the 

 seedling, which may be rare in "normal plants," but becomes common 



Fig. 78. — Lycopodium Selayo, L. Shoot-apex (5 + 6). 



in plants showing marked xerophytic adaptations, and even a specific 

 constant in certain forms. In such variations the " Fibonacci sense '' 



