306 RELATION OF PHYLLOTAXIS TO MECHANICAL LAWS. 



in Podocarpus (fig. 42) and Euphorbia Wulfenii (fig. 90), in 

 which a very considerable degree of "dorsiventrality," accompanied 



Fig. 106. — Euphorbia Uglandulosa. Spring shoot, system (3 + 4). 



by a well-marked sliding readjustment, is attained at a short 

 distance from the apex. Species of Sedum with so-called centric 

 leaves present a point of interest in that, while the primordia are 



