298 RELATION OF PHYLLOTAXIS TO MECHANICAL LAWS. 



of the radially elongated ovaries of Helianthus. Even in the case 

 of four cell-walls meeting at right-angles, such slipping normally 



Fig. 103. — Sedum pruinatum, Brot. Leafy shoot, system (5 + 8). 



obtains, and is always allowed for in a tissue-drawing, — the four 

 cell-walls at 90° tending to pull into two sets of three: this 



