GROUP IV. PHANEROGAMIA : ANGIOSPERM^. 



511 



Violaceae, Echinm, Lobelia, Orchidacese, the marginal flowers of 

 the inflorescences in some Umbellifera3 and the ray- florets of some 

 Composite). The degree of irregularity in these flowers varies 

 widely ; the irregularity may be very slight, due to the more active 

 growth of the leaves (perianth- leaves only, or stamens also) of 

 one half of the flower, either the posterior (e.g. Gladiolus), or the 

 anterior (e.g. Amaryllis), which causes an upward or a downward 

 curvature ; this is more marked in Dictamnus where the calyx 

 and corolla tend to form two lips, an upper and a lower; this 

 bilabiate form of flower is more f ally developed in the calyx and 

 corolla of the Labiatae, the corolla (personate, the lips being closed) 

 of the Scrophulariaceae, and of the Orchidaceaa and Lobelia. In 

 not a few cases the irregularity of the flower is increased by the 

 development of spurs from some portion of the perianth (e.g. 

 among Monocotyledons, Or- 

 chis, Rhinopetalum, from the 

 corolla ; among Dicotyledons, 

 Linaria, Viola, from the co- 

 rolla ; Pelargonium, from the 

 calyx). A remarkable mor- 

 phological feature is offered by 

 the flowers of Orchis and of 

 Lobelia which are resupinate ; 

 that is, in consequence of tor- 

 sion of the pedicel, the pos- 

 terior side of the flower becomes 

 anterior. The plane of sym- 

 metry is generally median in 

 these flowers. 



In some few cases the irregularity, leading to dorsiventrality, 

 is due, not to the unequal development of the floral leaves, but 

 to the configuration of the floral receptacle, so that the floral 

 leaves are not developed in a radially symmetrical manner (e.g. 

 Reseda, Papilionea?, Fig. 327). 



When in irregular flowers the single plane of symmetry is the 

 median plane, the flower is dorsi ventral : but there are other cases 

 (e.g. flowers of some Fumariaceae, Fumaria, Corydalis) in which 

 the single plane of symmetry is the lateral ; these flowers are 

 therefore not dorsiveritral, that is, they have not antero-posterior, 

 but lateral, asymmetry. The zygomorphic symmetry of a flower 

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



v. s. B. L L 



A 



FIG. 327. Diagram illustrating dorsiventral 

 symmetry in. leguminous flowers: A Vicia 

 Faba (Papilionese) : B Cercis Siliquastruni 

 (Caesalpiniese) : in both cases the odd sepal 

 is anterior : the plane of symmetry is median. 



