504 PART III. THE CLASSIFICATION OF PLANTS. 



Silene) with encyclic (tetra- or penta-merous) flowers, in that, though the ap- 

 parently outer stamens are directly antipetalous, the carpels are antisepalous. 

 This case seems to be connected with that of the Primulaceae (see p. 498), where 

 there is a single whorl of antipetalous stamens and the carpels are antisepalous, 

 through the Sapotacea where a whorl of antisepalous staminodes (Sideroxylon, 

 Lucuma) or of fertile stamens (Isonandra) is developed. It would, in fact, 

 appear that obdiplostemony may be the result of either pleiomery or pleiotaxy 

 taking place in a primitively isomerous monocyclic antipetalous androscium 

 (as in Primula) ; when the carpels, in an obdiplostemonous flower, are anti- 

 sepalous, it seems to be simply a case of pleiomery; when they are antipetalous, 

 it would seem to be a case of pleiotaxy, the androecium having become dicyclic 

 by the development of an inner whorl of stamens consequently involving a 

 change in the position of the gynaeceum. 



OUgotqxij) or a decrease in the number of whorls in a flower, is 

 frequently due to suppression. For instance, owing to the sup- 

 pression of one whorl of stamens in some Monocotyledons, either 

 the outer (some Haemadoraceae, also Cypripedium), or the inner 

 (Iridaceae, most Orchidaceae), the andrcecium is monocyclic. In 

 some cases a whole series is suppressed : for instance the corolla 

 may be absent (e.g. Glaux, among the Primulaceae ; Alchemilla, 

 Sanguisorba, among the Rosaceaa : some Caryophyllacese, such as 

 Sagina apetala, Scleranthus, etc.) : or the androecium or gynaeceum 

 (monoclinous flowers, such as those of Sedum Rhodiola, Rhamnus 

 cathartica, Hydrocharidaceae, ray-florets of Composites, etc.) : or 

 the whole perianth (Fraxinus excelsior). 



In most cases of oligotaxy in isomerous flowers, the relative 

 position of the remaining whorls is undisturbed : thus, in the 

 apetalous flower of Glaux, the typically antipetalous stamens 

 alternate with the sepals, and in that of Sanguisorba the stamens 

 are opposite to the sepals ; in the carpellary flower of Rhamnus 

 the carpels are antisepalous as in an ambisporangiate flower. 

 But this is by no means always the case : for instance, in the 

 apetalous flow^er of Alchemilla the stamens alternate with the 

 sepals, seeming to take the place of the missing petals : again, 

 the staminate flower of Sedum Rhodiola (Fig. 318) has rudi- 

 mentary carpels which are antipetalous, whereas in the carpellary 

 flowers the carpels are antisepalous, apparently occupying the 

 place of one of the missing staminal whorls; similarly in Halophila 

 (Hydrocharidaceae) the three carpels of the carpellary flower occupy 

 the same relative position as the three stamens in the staminate 

 flower. 



Alt'.ough it is true that, as explained in the foregoing paragraphs, both 



