Petalody of the stamens.—A petaloid condition of the stamens is one of the commonest of all malformations. A large number of so-called double flowers (flores pleni)[299] owe their peculiar appearance to this circumstance.
It is necessary to distinguish carefully this petaloid development of the stamens from the corresponding condition of the pistils, and from that kind of doubling which is a result of multiplication of the corolla, as in Datura, Campanula, Primula, &c. (flores duplices, triplices, &c.), or from that produced by true median prolification (flores geminati, &c.).
In cases of true petaloid development of the stamens there are usually numerous intermediate forms between that of the true petals and that of the perfect stamens; indeed, in Nymphæa, Canna, and in some other plants, such a transition occurs normally. Petalody of the stamens may occur either without material change in the flower or it may exist in combination or in conjunction with an increased development of parts (Multiplication), or with a similar change in the carpels, and it is either partial or complete.
Among the flowers in which petaloid development of the stamens happens most frequently may be mentioned those in which the calyx is normally coloured, as in Nigella damascena, Aguilegia, and Delphinium.
M. Alph. de Candolle, in the 'Neue Denkschriften,' 1841, described and figured a singular form of Viola odorata, known under the name of "Bruneau," in Switzerland, in which the stamens are absent, and their place supplied by a second row of petals, within which is a third series of petals, representing, says M. de Candolle, the inner row of stamens that theory suggests should exist in the natural condition. Moreover, the carpels in this variety are five in number instead of three. In Erica Tetralix the corolla may not unfrequently be found divided to the base into its constituent petals, and the place of the stamens occupied by a series of petal-like structures entirely destitute of anther.
In monocotyledonous flowers, especially those with a coloured perianth, the substitution of segments of the perianth for stamens occurs not unfrequently. M. Seringe has observed this in the stamens of Lilium Martagon, and there is in cultivation a variety of the white lily, Lilium candidum, sometimes called the double white lily, in which the segments of the perianth, in place of being arranged in two rows, are greatly increased in number, and disposed in a spiral manner. In these flowers, not only are the stamens and pistils thus modified, but also the upper leaves of the stem. In so-called double tulips there is likewise a replacement of stamens by coloured segments of the perianth, but this happens generally in connection with an increase in the number of organs. Moquin-Tandon remarks having seen in a garden in the environs of Montpelier a tulip, the stamens of which showed all possible stages of transition between the form proper to them and that of the perianth. The pistil in this case was transformed into several small leaves. Similar appearances have been observed in Iris, Hyacinths, Narcissus, Colchicum, and Crocus. M. Fournier[300] describes a flower of Narcissus Tazetta from within the normal perianth of which sprang a second one, equally provided with a cup and occupying the space usually filled by the stamens. Flowers of Narcissus poeticus may also be met with in which the stamens are replaced by six distinct segments exactly resembling those of the perianth in miniature.[301]
Fig. 154.—Double columbine, Aquilegia—petalody of the filament.
From an examination of these flowers it becomes evident that petalification is brought about in different flowers in different ways; sometimes it is the filament which becomes petaloid, sometimes the anther-lobes, while at other times it is the connective which assumes the appearance of petals.[302] For instance, in Solanum tuberosum, S. Dulcamara, in Anagallis, in Fuchsia, and some other plants, the anther-lobes themselves become petaloid, while the filament remains unchanged.