96 RELATION OF PHYLLOTAXIS TO MECHANICAL LAWS. 



(34+55) system, uneven orthogonal figures will, it is true, be 

 produced, and it might be conceivable that the plant could adjust 

 these to circular primordia as growth proceeded, so long as the 

 direction of the curves remains the same, but it will be found that 

 the genetic spiral is reversed.* 



Fig. 34.— Table showing direction of contact parasticliies, and the genetic 

 spiral for successive systems of the Fibonacci series. 



There is clearly no evidence whatever that such reversal occurs 

 in normal growth, since the genetic spiral {Cynara) may be checked 



* This remarkable property of the curved systems, by which the spiral selected 

 as the ontogenetic spiral is reversed in successive ratio-systems, is tabulated in 

 fig. 34 (Part I. p. 70). Comparison of the structural diagrams for (5 + 8) and 

 (8 + 13), for example, with the same direction of parastichy curves, shows that the 

 displacement of the first member of successive cycles in the latter case follows the 

 direction of the genetic spiral, but in the former is in the reverse direction. 

 These appearances may be readily checked on the dry cones of Pinus austriaca 

 (8 + 13) and Pmus laricio (5 + 8). 



Such reversal will again lend additional complexity to phenomena of homo- 

 dromy and heterodromy in lateral shoots. 



