RISING PHYLLOTAXiS. l3l 



present a phyllotaxis (2 + 3) which is evidently correlated 

 with the assumption of a lower bulk-ratjo. The transition 

 is abrupt, and takes place at the member numbered 12, 

 which is thrown forward to such an extent, that the 

 genetic spiral at first appears to have been reversed ; the 

 new curve established at this point allows No. 14 to fill 

 in the gap behind 12. The parastichies are reversed and 

 a very definite distortion of the system is apparent at the 

 junction of the two systems. 



II. Saxifraga umbrosa (London Pride). Young shoots produce 

 leaves in a rosette of the type (2 + 3), older ones may 

 exhibit (3 + 5). Sections of a bud taken in January show 

 the new year's growth already laid down within the 

 rosette of the previous season and already terminated by 

 a developing inflorescence. In such cases a break occurs 

 at the junction of the two seasons' growth (fig. 52). 

 This is exaggerated, owing to the fact that the last formed 

 leaves of the previous season were poorly developed and 

 never attained adult form (11 and 12). The same break 

 in the genetic spiral, and reversal of the parastichy curves, 

 is observable : the genetic spiral continues in a right-hand 

 . direction, but the long curves are now differing by 3, 

 the short by 5 ; the dislocation of the junction is shown 

 by the curious relations of the members numbered 

 (along the curves) 13 and 15 ; and this, taken into con- 

 nection with the rudimentary condition of 11 and 12, 

 militates against any view that the (2 + 3) appearance of 

 the older members is merely an effect of sliding growth 

 due to the formation of a sheathing leaf-base. 



These two examples suffice to show — 



( 1) A new system may be originated at a new period of growth 

 producing similar members on a presumably increased axis. 



(2) That on a constant axis the bulk-ratio may be lowered so 

 as to admit of a system which has no direct relation in the 

 distribution of its curves to the previous construction. 



The latter case is of great importance in dealing with the 

 insertion of floral members in floral structures, while the former 



