GROUP V. AXGIOSPERM.E. 



455 



lariacese, Labiatse, some Caprifoliacese, Violacese, Echium, Lobelia, 

 Orchidaceae, the marginal flowers of the inflorescences in some 

 Umbelliferae and the ray-florets of some Compositae). 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 curva- 

 ture; 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 fully developed in the calyx and corolla 

 of the Labiatse, the corolla 

 (personate, the lips being 

 closed) of the Scrophulari- 

 acese, and of the Orchidacese 

 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, 

 Orchis, Rhinopetalum, from 

 the corolla ; among Dicotyle- 

 dons, Linaria, Viola, from the 

 corolla ; Pelargonium, from 

 the calyx). A remarkable 

 morphological feature is 

 offered by the flowers of 

 Orchis and of Lobelia which 

 are resupinate ; that is, in consequence of torsion of the pedicel, 

 the posterior side of the flower becomes anterior. The plane of 

 symmetry 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.y. 

 Reseda, Papilioneae, Fig. 272). 



When in irregular flowers the single- plane of symmetry is the 

 median plane, the flower is dorsiventral : 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 



FIG. 271. Dorsiventral flower of a Heracleu 

 (mag.) 



