36 THE STRUCTURE OF FLOWERS. 



central floret of the cyme has often a higher number than that 

 of the lateral ones ; so that if they be 6-merous, the central 

 flower will be 7-merous. Agapantlms, amongst Monocoty- 

 ledons, is another instance, its flowers ranging from 6 to 8 in 

 the number of parts in the whorls. 



OcTAMEROUS Whorls. — A whorl of eight parts is not 

 common ; but it appears in Chlora and in the corolla of Dry as 

 octopetala, in which it may be a cycle of the f phyliotaxis. 

 In other cases it is a combination of two whorls, which, as a 

 rule, can be easily distinguished as the stamens in the 0)ia- 

 gracece, or it may be due to symmetrical change. 



Enneamerous Whorls. — The number 9, like 6, 7, and 11, 

 corresponds to no cycle of any one of the usual forms of leaf- 

 arrangement, and is proportionately rare. It may occur as a 

 combination of three cycles of three each, and perhaps this 

 will account for it when it occurs in Trientalis, and the 

 androecium of Mercurialis. The stamens of Butomus are 

 also nine in number. 



Decamerous Whorls. — The number 10 never occurs 

 except as the union of two whorls of five in each, as in the 

 androecium of Legitminosce. 



ExDECAMEROUS Whorls. — Like 7, the number 11 might 

 occur if the series -§-, i, f , tt? ^tc, was as frequently repre- 

 sented as ^, ^, f, f, etc., when "sevens " would be as abun» 

 dant as " fives " are now. I do not know of a case where it 

 could reasonably be referred to such an origin. When it 

 does occur, as in Cupliea, it is clearly due to an arrest of one 

 stamen through insect agency. Broiunea is said also to have 

 sometimes 11 stamens ; if so, this would undoubtedly be due 

 to numerical increase. 



DoDECAMEROUS Whorls. — The number 12 closely verges 

 on the " indefinite," w^hich simply means a more or less 

 numerous series of cycles of the same kind. Neverthe- 



