ASYMMETRY. 75 



VI. Asymmetry. 



Symmetry and Asymmetry. 



The whole subject of phyllotaxis is thus restricted to a question 

 of the symmetrical or asymmetrical growth of the plant-apex during 

 the process of originating the impulses which give rise to new 

 centres of lateral growth. 



That the framers of the original spiral theory were undoubtedly 

 correct in demanding that symmetry is in all cases secondary, and 

 asymmetry the primitive condition, is shown by comparative mor- 

 phology ; and transition, if not actually ontogenetic, is clearly so 

 phylogenetically. All Phanerogams, Cryptogams and the bulk of 

 the Algee, with whorled series of lateral members, either commence 

 with an asymmetrical condition or show traces of it in subsequent 

 development ; thus, among Angiosperms, in some types the vegeta- 

 tive system becomes symmetrical while the spiral condition is 

 retained in the reproductive members {Calycanihus) ; in others the 

 latter are wholly whorled, whUe the former retain the primitive 

 asymmetrical condition (AquUegia) : even when both become wholly 

 whorled, the presence of a pentamerous flower, or a type derived 

 from such a structure (Labiatae), which is a form which does not 

 mechanically pack in the sense that 2-3-4 and 6-merous types do, 

 these being referable to rhomboidal and hexagonal systems, is 

 sufficient evidence of a primitive quincuncial construction. 



Among lower forms, the Dasycladaceae alone present types in 

 which symmetrical construction possibly obtains from the earliest 

 stages (iV«omem), and even in these the eoenocytic structure is itself 

 admittedly secondary. 



