450 PART IV. CLASSIFICATION. 



moner cases of oligomery are to be found in the whorls of 

 sporophylls, especially in the gynseceum : for instance, the 

 typically pentamerous flower of the Saxifragaceas is heterocyclic 

 because of the oligomerous (dimerous) gynseceuin ; similarly, in the 

 Scrophulariacese, the androecium is generally, and the gynseceum is 

 always, oligomerous, the former consisting of but two or four 

 stamens, the latter of but two carpels. Pleiomery is of less 

 frequent occurrence : however in the Cruciferse (Fig. 266) the 

 whorls of the calyx, the outer whorl of stamens, and the 

 gynseceum, are dimerous, but the corolla and the inner whorl of 

 stamens are tetramerous and hence pleiomerous : similarly, one or 

 more whorls of the androBcium in the Papaveracese and Poly- 

 gonacese are pleiomerous : and probably in other cases where the 

 number of the stamens is twice that of the petals or sepals, that 

 is, where the flower is diplostemonous, the condition is due rather 

 to pleiomery (duplication) of a single whorl than to the develop- 

 ment of two whorls as is usually assumed (see below, under 

 pleiotaxy). Pleiomery of the corolla is common in double flowers. 



Heterornery necessarily affects the alternation of the floral 

 leaves of the successive whorls. Thus, in the Cruciferse, where 

 the calyx consists of two alternating dimerous whorls, and the 

 corolla of a single tetramerous whorl, the four petals alternate 

 with the four sepals just as if the sepals all belonged to a single 

 whorl. When, as is very frequently the case, the gynseceum is 

 oligomerous, the carpels (or carpel) present do not appear to occupy 

 any definite position with regard to the preceding organs. 



The Number of Whorls in the Flower. The simplest case is 

 that in which each series of floral organs calyx, corolla, androe- 

 cium, gynseceum occupies a single whorl, or is monocyclic : this 

 is realized in a few natural orders, either accompanied with 

 regular alternation (e.g. Caprifoliacese generally, Iridacese, Orchi- 

 dacese), or with antipetalous stamens (e.g. Rhamnacese, Ampeli- 

 dacese). In this case the flower is tctracyclic. 



More commonly one or more of the series may occupy two 

 whorls, or be dicyclic. This is generally the case when the whorls 

 are dimerous (e.g. both corolla and androacium of Oleacese and 

 Fumariaceae ; corolla of Papaver ; calyx and androecium of Cruci- 

 ferse; perianth of Urtica and Morus). Where the whorls are 

 trimerous the dicyclic condition is frequent : thus in the majority 

 of Monocotyledons there are two whorls of stamens whilst all the 

 other series of the flower are monocyclic, so that the flower is 



