FLORAL SYMMETRY. 



177 



as a pattern trimerous or ternary flower; these being simply 

 isomerous, and of one circle of each kind. And the whole 



relation of the parts, viewed as 

 modified leaves on the common 

 axis, may be exhibited in such a 

 diagram of a pattern isostemonous 

 5-merous flower as that displayed 

 in Fig. 328. 



324. Diplostemonons Type. The 

 foregoing patterns are selected 

 upon the idea of the greatest 

 simplicity consistent with com- 

 pleteness. But extended observation leads to 

 the conclusion that the typical flower in nature 

 has two series of stamens, as it has two series in 

 the perianth ; that is, 

 as many stamens as 

 petals and sepals taken 

 together. 1 As the 

 petals alternate with 

 the sepals, so the first 

 series of stamens al- 

 ternates with the pet- 

 als, the second series 

 of stamens alternates with the first, and the pistils or carpels 

 when of the same number alternate with these. Thus the outer 

 series of stamens and the carpels normally stand before (are 



1 This view of the symmetry of the flower was first taken by Brown 

 (Obs. PI. Oudney, in Denham and Clapperton Trav. 1826, reprinted in Ray 

 Soc. ed. of Collected Works, i. 293). It is true that Brown declares the 

 same of the pistils ; but that is not made out. The evidence of this doctrine 

 is to be gathered from a large and varied induction ; from the general pres- 

 ence of the two sets of stamens, and no more, in petaloideous Monocotyle- 

 dons ; the unaltered position of the carpels (before the sepals) when the 

 inner set of stamens is wanting, as in the Iris Family ; the very common 

 appearance in haplostemonous flowers among the Dicotyledons of vestiges 

 of a second series, or of bodies which may be so interpreted. The andrcecium 

 or the blossom is said to be 



Isostemonous or Haplostemonous when the stamens are of one series, equal 

 in number to that of the ground-plan of the blossom ; 



Diplostemonous, when there are two series, or double this number. 



FIG. 328. Ideal plan of a plant, with the simple stem terminated by a symmetrical 

 pentamerons flower; the different sets of organs separated to some distance from each 

 other, to show the relative situation of the parts. One of each, namely, a, a sepal, b. 

 a petal, c, a stamen, and d, a pistil, also shown, enlarged. 



FIG. 329. A pentamerous diplostemonous flower of Sedum. 



