300 RELATION OF PHYLLOTAXIS TO MECHANICAL LAWS. 



edges (c/. valvate prefloration), and there is no reason why the 

 slip should take place in one way more than the other. 



Fig. 104. — Sedum reflexu/m, L. Perennating shoot, system (3+4) = 7-spired : 

 the vascular bundles follow the spiral of dorsiventrality, which is here also the 

 ontogenetic spiral. 



