78 THE PHENOMENON OF 



corollas, will not be contested although we omit to 

 demonstrate it by a numerical comparison, which of 

 course would have to be based on a determinate and 

 perfectly known flora. Splendid and conspicuous exam- 

 ples of it are furnished by the genera Datura (e. g. 

 D. arborea], Convolvulus, Gentiana (e. g. G. acaulis), 

 Campanula, Cucurbita, PcBonia, Dillenia, Hibiscus, &c. 

 This relation holds good also in small-flowered plants, as, 

 for instance, in Vitis, in the Umbelliferse and the Com- 

 positae. Even in the Monocotyledons, where generally 

 speaking the abrupt differentiation of calyx and corolla 

 does not exist, the inner three segments of the perianth 

 are frequently distinctly longer that the outer three, as, 

 for instance, in Lachenalia and Vropetalum, of the Lily 

 family, in all the Bromeliaceae, Commelyneae, Cannaceae, 

 and Alismaceae. The rarer occurrence of petals shorter 

 than the calyx, is explained, in many cases, by an intro- 

 version of one formation into the other, whereby the 

 maximum of longitudinal development becomes displaced. 

 Thus, in many Ranunculaceae (e. g. Trollius, Nigelld) the 

 petaloid calyx is succeeded by shorter and more contracted 

 petals approximating to the stamens. In other families 

 also occur isolated genera, with a petaloid calyx, the 

 leaves of which are longer than the true petals ; e. g. in 

 Fuchsia (calyx mostly bright-red, rarely white, petals 

 mostly violet), Ribes (Chrysobotrya), Commarum, and 

 ChimonantJms. The last-named genus has about eight 

 delicate yellow sepals, followed by an equal number of 

 dark purple-red petals, only half as long. In other cases 

 the small size of the petals is connected with a tendency, 

 prevailing in many families, to suppression of the corolla 

 (Sibbaldia, Sagina sp., Paronychia, Gnidia, Santalum, 

 &c.), to which we shall return hereafter. 



No farther increase of length takes place within the 

 corolla itself, at least I am unacquainted with any instances 

 of it ; on the other hand, the decrease which succeeds to 

 the maximum of longitudinal development in the second 

 member of the flower, not unfrequently commences even 



