PHANEROGAMIA 



507 



(Fig. 483, 2). When the concave floral axis, the margin of which 

 bears the androecium, becomes adherent to the gynaeceum, the latter 

 is said to be INFERIOR while the flower is described as EPIGYNOUS. 



The regions of the axis or of other parts of the flower which 

 excrete a sugary solution to attract the pollinating animal visitors 

 are called NECTARIES. Their biological importance is considerable. 



In a typical angiospermic flower the organs are thus arranged in 

 five alternating whorls, of which two comprise the perianth, two the 

 androecium, while the gynaeceum consists of one whorl. The flower 

 is PENTACYCLIC. The number of members is either the same in each 

 whorl (e.g. three in a typical Monocotyledon flower, or five in a typical 

 Dicotyledon flower), or an increase or decrease in the number takes 

 place. This is especially the case with the whorls composing the 

 androecium and gynaeceum. 



Some of the more frequent deviations from the floral structure described above 

 may be referred to here. Variation in the number of whorls is common. A 

 diminution in the number may result from the absence of one kind of sexal organ 

 in diclinous flowers (e.g. Myris^ica}, or from the absence of one of the two wh'orls 



B 



Fio. 484. A, ActinoniorpHic flower of Ueranium sangniin-uni. U. Zygoinoi pliic flower of 

 Viola tricolor. ' , Asymmetrical flower of Canna indica. 



composing the androecium or perianth (Compositae). Flowers in which the 

 androecium consists of only one whorl are termed HAPLOSTEMONOU.S, those with 

 two whorls of stamens DIPLOSTKMONOUS. On the other hand, the number of whorls 

 may be increased, and this may affect the androecium (A'osa), the gynaeceum (Punica 

 gra-natum), or the perianth (Hayenia abyssinica). Another simple modification 

 concerns the position of the whorls. The outer whorl of the androecium, in Erica, 

 for instance, does not alternate with the segments of the corolla but the stamens 

 stand directly above the latter. Such an androecium is distinguished as OBDIPLO- 

 STEMONOUS from the ordinary DIPLOSTEMONOUS type. 



Variations in floral symmetry are more important both biologically and with 

 regard to the general habit of the flower. Those flowers which can be divided 

 into similar halves by more than two planes passing through the axis are termed 

 RADIALLY SYMMETRICAL or ACTiNOMORPHic (Fig. 484 A}. When a symmetrical 



