296 RELATION OF PHYLLOTAXIS TO MECHANICAL LAWS. 



are thus rendered increasingly obvious; so much so, that when 

 the sliding effect is considerable they can alone be readily checked. 

 From this standpoint it is easy to introduce the phenomena of 

 normal sliding-growth into the construction diagram, as in fig. 110 

 (5 + 8), or again as in the (8 + 13) system of fig. 100, in which the 



Fig. 102. — Sedum acre, L. Perennating bud, system (3 + 5). 



2W-S 

 scheme consists of a normal phyllotaxis system plotted, however, 



with a curve of the second type, — of uniformly retarded growth, 

 — which conveys the information that a progressive retardation in 

 the radial rate of growth of the system as a whole produces the 

 effect of a progressive " dorsiventrality " in the leaf -members. 

 But while the progressive increase of dorsiventrality in the 



