GROUP V. AXGIOSPERM.E. 



457 



Tlie Floral Organs. 



The Perianth is completely absent, that is, the flower is achlamy- 

 dcous, in a few families (e.g. Piperacese, Aracese, Graminaceae, many 

 Cyperacese, Salicacese). When present, it is usually differentiated 

 into calyx and corolla, the flower being termed dicldamydcous or 

 biscriate : when the calyx and corolla clearly differ from each 

 other in colour, texture, etc., the flower is said to be heterochlamy- 

 dcous for instance, when the calyx is green and the corolla highly 

 coloured (as in most* Dicotyledons, and in some Monocotyledons 

 such as Tradescantia and Commelyna) ; or when the calyx is col- 

 oured (petaloid) and the petals reduced to nectaries (as in Helleborus 

 and other Ranunculacese). When the perianth-leaves are all alike, 

 the flower is said to be homochlamydeous. This condition 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 Monoco- 

 tyledons 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 monoclilamy- 

 dcous. The flower may be monochlamydeous, because, though 

 typically dichlamy- 

 deous, either the 

 calyx or the corolla 

 is suppressed (e.g. 

 calyx suppressed in 

 some Umbelliferse 

 and Composite ; co- 

 rolla suppressed in 

 most Thymelseacese, 

 Paronychiese, Glaux, 

 some Rosacese such 

 as Alchemilla and 

 Sanguisorba); where 

 the corolla is sup- 

 pressed or rudiment- 

 ary the calyx is 



frequently petaloid (e.g. Clematis, Anemone, Caltha, and other 

 Ranunculacese) : or the flower may be monochlamydeous merely 

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

 generally sepaloid (e.g. Urticacese, Betulacese, Chenopodiacese, etc.), 

 or petaloid '(e.g. some Amarantaceae). 



I. Floral diagrams illustrating asymmetry. 

 A Dorsiveutrally asymmetrical hemicyclic flower of Del- 

 phinium Ajaels : B Dorsiventrally asymmetrical heterocy- 

 clic flower of Tropoeolum majug : br subtending bract ; 

 p- t >, prophylla. (After Eichler.) 



