GROUP IV. — PHANEROGAMIA : ANGIOSPERM^, 601 



former is frequently realized (e.g. many Monocotyledons). The 

 heterocyclic condition is due either to the number of members in 

 one or more of the whorls being smaller (oUgomery) or greater (pleio- 

 mery) than that which is the typical number. The commoner cases 

 of oligomery are to be found in the whorls of sporophylls, especi- 

 ally in the gynoeceum : for instance, the typically pentamerous 

 flower of the Saxifragacea3 is heterocyclic because of the oli- 

 gomerous (dimerous) gynaeceum; similarly, in the Scrophula- 

 riaceae, the andrcecium is generally, and the gynaeceum is always, 

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

 latter of but two carpels. Pleiomery is of less frequent oc- 

 currence : however in the Cruciferae (Fig. 315) the whorls of the 

 calyx, the outer whorl of stamens, and the gynaeceum, are 

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

 tetramerous and hence pleiomerous : similarly, one or more whorls 

 of the andrcecium in the Papaveracese, Phytolaccaceee, and Poly- 

 gonaceae, 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. 



Heteromery necessarily affects the alternation of the floral leaves 

 of the successive whorls. Thus, in the Cruciferae, 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 gynaeceum is oligomerous, the 

 carpels (or carpel) present do not appear to occupy any definite 

 position with regard to the preceding organs. 



The Numher of Whorls in the Floicer. The simplest case is that in 

 which each series of floral organs — calyx, corolla, andrcecium, gynae- 

 ceum — occupies a single whorl, or is monocyclic : this is realised in 

 a few natural orders, either accompanied with regular alternation 

 (e.g. Asclepias, Cornus, Caprifoliaceae generally, Iridaceae, Orchi- 

 daceae), or with antipetalous stamens (e.g. Rhamnaceae, Ampeli- 

 daceae). In this case the flower is tetracyclic. 



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 andrcecium of Oleaceae and 

 Furaariaceae; corolla of Papaver : calyx and andrcecium of Cruci- 



