45G 



PART IV. CLASSIFICATION. 



therefore not dorsiventral, that is, they have not an tero- posterior, 

 but lateral, asymmetry. The zygomorphic symmetry of a flower 

 is indicated in its floral formula by symbols ; when the plane of 

 symmetry coincides with the median plane the symbol ^ is used, 

 and when it coincides with the lateral plane the symbol ->. 



Sometimes regular flowers are developed by plants which 

 usually produce irregular flowers : these exceptional flowers are 

 termed pcloria. This is due in some cases to the fact that the 

 primitive number and arrangement of the floral organs is not 

 disturbed by the irregular development of the parts which 

 usually takes place : such cases are distinguished as regular 

 peloria (e.g. Viola, Gloxinia, Labiatse, etc.). In other cases the 

 peloric flower is to some extent the result of the symmetrical 



development of the irregularity 



O o (e.g. the development of five 



spurred petals and five sta- 

 mens in Linaria). Dorsiven- 

 tral flowers are, generally 

 speaking, such as are borne 

 laterally on the inflorescence ; 

 whilst the terminal flowers 

 (which may be regarded as 

 peloric) are frequently regular. 

 Peloric lateral flowers are, 

 however, known to occur. 



There remain to be con- 

 sidered those flowers which 

 cannot be symmetrically di- 

 vided in any plane : such flowers are asymmetric. Amongst these 

 are to be included most of the acyclic or hemicyclic flowers in 

 which the number of members is high and the divergence vari- 

 able (e.g. Calycanthus, some Ranunculacese, etc.) : the asymmetry 

 of most of these is approximately, though not quite accurately, 

 actinomorphic, but in some it is dorsiventral (e.g. Delphinium, 

 (Fig. 273 A,) Aconitum). Asymmetry is rare in cyclic flowers, 

 but is to be found in some heterocyclic flowers : for instance, in 

 Tropseolum, (Fig. 273 5,) Canna and other Marantacese, Valeriana 

 and other Valerianacese, where the asymmetry is dorsiventral and 

 is due to oligomery and irregularity combined, whilst in other 

 cases (e.g. some Paronychiese), it is due merely to oligomery. 



FIG. 272. Diagram illustrating dorsiventral 

 symmetry in leguminous flowers: A Vicia 

 Faba, (Papilionese) : B Cercis SiUquastrum 

 (Casalpinieae) : in both cases the odd sepal 

 is anterior : the plane of symmetry is median. 



