184 THE STRUCTURE OF FLOWERa 



CHAPTER XX. 



THE EMERGENCB OF THE FLORAL WHORLS. 



Theoeeticallt, as already stated, a perfect flower should or 

 might be composed of six whorls, it its parts be not spirally 

 disposed, — the perianth, andrceciam, and gynoecium each 

 consisting of two verticils. The very general rule for their 

 emergence from the axis is centripetal. The subsequent 

 rates of development of the several whorls may vary con- 

 siderably, so that one part which emerged first, or at least 

 very early, may be late or the last to arrive at maturity. 



The calyx or outermost whorl of the perianth when 

 present is nearly always the first to appear, and to grow 

 rapidly to a relatively large size, and thus protects the more 

 rudimentary parts within it ; but if it ultimately remains 

 rudimentary itself, or, it may be, is not entirely arrested, then 

 it is the corolla which first emerges, the function of pro- 

 tecting the essential organs being relegated to it. Such is 

 the case with the Compositcp, ValerianecB, etc. 



The corolla, with rare exception, emerges before the 

 stamens, though it is very generally rapidly passed in 

 development by the latter organs. In Lopezia and Primula, 

 however, the stamens emerge first ; and this has led some 

 botanists* to regard the petals of the last-named plant as 



• For references and literature on the stmotnre of Primulacew, see 

 Masters's paper. On some PoinU in the Morphology of the Primulacew, 

 Trans. Lin. Soc., 2nd series, Botany, vol. i., p. 285. 



