GROUP IV. PHANEROGAMIA : ANGIOSPERMvE. 



513 



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

 sometimes homochlamydeoup, 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 monochlamydeous. 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 Composite; corolla suppressed in most Thymelaeaceae, 

 Paronychiea3, Glaux, some Rosaceae, such as Alchemilla and 

 Sanguisorba) ; wh^re_the_cprolla , is suppressed or rudimentary the 

 calyx_ is Jr^iientij^etaloid (e.g. Clematis, Anemone, Caltha, and 



FIG. 328. Floral diagrams illustrating asymmetry. A Dorsiventrally asymmetrical 

 heinicyclic flower of Delphinium Ajacis : B Dorsiventrally asymmetrical heterocyclic flower 

 ofTropceohtm majus : C Asymmetry due to oligomery in Anycliia dichotoma (Paronychieae): br 

 subtending bract ; p-p, a j3 propbylla; st stipules of bract and prophylla. (After Eichler.) 



other Ranunculacese) : or the flower may be monochlamydeous 

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

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

 Chenopodiacese, etc.), or petaloid (e.g. some Amarantaceae, Phyto- 

 laocaceae, Nyctaginaceas). 



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 



