GROUP IV. — PHANEROGAMIA : ANGIOSPERMiE. 



513 



may be due to different causes in different cases : the flower is 

 sometimes homochlamydeous, even though calyx and corolla are 

 differentiated, because the sepals and petals are very similar, as 

 in most Monocotyledons where the sepals are often petaloid : in 

 other cases the flower is homochlamydeous, because only one 

 series of perianth-leaves is developed ; that is, because the flower 

 is ononochlamijdeous. The flower may be monochlamydeous be- 

 cause, though typically dichlamydeous, either the calyx or the 

 corolla is suppressed {e.g. calyx suppressed in some Umbelliferae 

 and Compositae; corolla suppressed in most Thymelaeaceee, 

 Paronychieee, Glaux, some Rosaceae, such as Alchemilla and 

 Sanguisorba) ; where the corolla is suppressed or rudimentary the 

 calyx is frequently petaloid (e.g. Clematis, Anemone, Caltha, and 



^.~ 



Fig. 328.— Floral diagrams illustrating asymmetry. A Dorsiventrally asymmetrical 

 heiiiicyclic flower of Lelphinium Ajacis : B Dorsiventrally asymmetrical heterocyclic flower 

 of TropcEolum majus : C Asymmetry duetooligomery in.4n}/c'tiadic?iotoma(Paronychie£e): br 

 subtending bract ; p-p, « /3 propbylla; st stipules of bract and prophylla. (After Bichler.) 



other Ranunculaceae) : or the flower may be monochlamydeous 

 merely because the perianth is undifferentiated (simple), and is 

 then generally sepaloid (e.g. Urticaceee, Betulaceae, Proteaceee, 

 Chenopodiaceee, etc.), or petaloid (e.g. some Amarantacea?, Phyto- 

 laccaceae, Nyctaginaceoe). 



It is not always easy to determine whether a homochlamydeous 

 flower is dichlamydeous or monochlamydeous ; but the decision is 

 facilitated by the consideration that, as a rule, the calyx and 

 corolla each consist of a single whorl of perianth- leaves in the 

 Monocotyledons, whereas in Dicotyledons the calyx generally con- 

 sists of two whorls. Hence, in the absence of contrary informa- 

 tion afforded by its development, a homochlamydeous flower having 



