GSOSS ANATOMY OF TEE ANQIOSPEBMS. 305 



These wliorls usually contain definite numbers of organs in 

 each ; in many cases the numbers are the same for all the whorls 

 of the flower (isomerous flower) ; when the numbers are different, 

 the flower is said to be heteromerous. 



The terms which denote these numerical relations are : monocyclic, 

 applied to a flower having only one cycle ; hicyclic, two cycles ; iri- 

 cyclio, three cycles ; tetracyclic, four cycles ; pentacyclic, five cycles, 

 etc.; monomerous, applied to flowers each cycle of which contains one 

 member ; dimerous, two members ; trimerous, three members ; tetram. 

 erons, four members ; pentamerous, five members, etc. 



Floral Formulae-— These relations can be briefly indicated by using 

 symbols and constructing floral formulae, as follows : 



Cas, Cot, Ane, Gns = a tetracyclic pentamerous flower ; 

 Caa, C03, Ana + s, Gus = apentacyclic trimerous flower. 



Most commonly the members of one whorl alternate with those ot 

 the whorls next above and below ; in a few cases, however, they are 

 opposite (or superposed) to each other. 



Floral Diagrams — These relations may be indicated by a modifica- 

 tion of the floral formulse given above, as follows, where the mem- 

 bers are alternate : 



Gn 



An 



An 



Co 



Ca 



B 



When they are opposite, the arrangement is as follows : 



Gu 



An 



Co 



Oa 



B ■ 



In both these diagrams the position of the parts of the flower with 

 respect to the flowering axis is indicated by the position of the bract 

 B, which is always on the anterior side, while the axis is always pos- 

 terior. 



Symmetrical Flowers — When all the members on each whorl are 

 equally developed, having the same size and form, the flower may be 

 vertically bisected in any plane into two equal and similar halves ; it 

 is then aetinomorphic (= regular and polysymmetrical, Fig. 199). 

 When the members in each whorl are unlike in size and form, and 

 the flower is capable of bisection in only one plane, it is zygommphio 



