SYMMETRICAL NON-CONCENTRATED TYPE. 163 



VI. Symmetrical Non-concentrated Type. 



Like the preceding, a comparatively rare formation, this forms 

 the system known as superposed whorls. 



Similarly, also, it is more general as expressed in terms of cells, 

 than of lateral members of more massive character, being, in fact, 

 the conceivably theoretical case for the primary arrangement 

 of isodiametric cells in the growing points of all Phanerogams, 

 and well seen in the unmodified tissues of many roots {cf. Zea). 

 The remarkable absence of concentration systems in cell-tissues, 

 while these form the characteristic feature of the arrangement 

 of massive primordia, affords confirmation of the hypothesis that 

 concentration is always derived secondarily through a spiral 

 construction. The presence of superposed whorls in the vegetative 

 shoot is doubtful, but in floral mechanisms it is more general, 

 and in a large number of cases generally accepted as being of 

 secondary origin. From the standpoint of the theory of Schimper 

 and Braun, superposition of the members of successive whorls 

 naturally followed from their constructions for superposed spiral 

 cycles, and any deviation from such superposition had to be 

 accounted for by prosenthesis. The present standpoint, that 

 alternation is the normal and primitive condition, thus renders 

 many phylogenetic generalisations improbable. The fact that 

 in higher plants, whorled types appear to be always reached 

 vid a concentrated asymmetrical construction, suggests, therefore, 

 that true superposition is always secondary. The logical con- 

 sequences of such a view have an important bearing on the 

 structure of floral organs. It becomes necessary to distinguish 



