Petaloid coloration of the ordinary leaves, or of the bracts, is mentioned under the chapter relating to colour.
Petalody of the calyx—Calycanthemy.—As with the bracts, so the calyx in certain instances is naturally coloured, as in Delphinium, Tropæolum, and others. In Mussænda, Calycophyllum, Usteria, &c., one or more of the calyx lobes become enlarged normally. Considered teratologically, petaloid coloration of the sepals is either general or partial; in the latter case the nerves retain their green colour longest. There is in cultivation a variety of the primrose called Primula calycanthema, in which the upper part of the calyx becomes coloured, so that the flower seems to have two corollas placed one within the other; a similar thing happens in Mimulus, in which plant, as the calyx is permanent while the corolla is deciduous, the coloured calyx is a great advantage in a horticultural point of view. Morren[296] says that in order to produce the fine colour of the calyx of Primula officinalis (var. smaragdina) the Belgian gardeners cut away the corolla in a very early stage, and that in consequence the colouring matter proper to the corolla is developed in the tube of the calyx, the edges of the limb remaining green, the middle of the limb being purple (Primula tricolor).
Fig. 153.—Flower of Mimulus, with petaloid calyx.
Under this head may be mentioned the occurrence of tubular sepals in place of the ordinary flat ones in Helleborus olympicus; only two of the sepals were thus affected in a specimen recently observed—a third exhibited an intermediate condition.
The normal coloration of the calyx occurs most frequently in polysepalous calyces; teratological coloration, on the other hand, occurs especially in gamosepalous flowers. This assertion is borne out by the frequency of the change in the plants already mentioned, and also in the following:—Campanula persicifolia, Anagallis arvensis, Gloxinia, Syringa persica,[297] Calceolaria, &c. &c. In the last-named plant one or more of the lobes of the calyx may frequently be seen replaced by a slipper-like petal.
Among polysepalous plants petaloid sepals have been observed in Ranunculus auricomus, Rubus cæsius, &c. Fleischer also describes a case of this kind in Carum carui.[298]
It will be seen from the above that in the majority of cases there is no real metamorphosis or substitution of petal for calyx, but simply an alteration in colour; nevertheless, a change in form may accompany a change of colour: this happens especially if there has been any displacement of organs. Thus, if, in an orchidaceous plant, a sepal be displaced from any cause, or a petal be twisted out of its natural position to occupy the place of an absent sepal, that petal will be sepal-like in form, and vice versâ.