Cornus mas and C. suecica sometimes show a triple involucre.[428] Irmish[429] records an analogous case in Anemone Hepatica, wherein the involucre was doubled. Similar augmentation occurs in cultivated Anemone. In addition to the plants already mentioned, Engelmann[430] mentions as having produced bracts in unwonted numbers, Lythrum Salicaria, Plantago major, Veronica spicata, Echium vulgare, Melilotus arvensis, and Rubus fruticosus.
It must here be remarked that this great number of the bracts occurs naturally in such plants as Godoya, in which the bracts, or, as some consider them, the segments of the calyx, are very numerous, and arranged in several overlapping segments.
In some of the cultivated double varieties of Nigella the finely divided involucral bracts are repeated over and over again, but on a diminished scale, to the exclusion of all the other parts of the flower.
Pleiotaxy or repetition of the calyx.—The true calyx is very seldom affected in this manner, unless such organs as the epicalyx of mallows, Potentilla, &c., be considered as really parts of the calyx.
In Linaria vulgaris Rœper observed a calyx consisting of a double series, each of five sepals, in conjunction with other changes.[431] It is also common in double columbines, delphiniums, nigellas, &c.
In the 'Revue Horticole,' 1867, p. 71, fig. 9, is described and figured by M. B. Verlot a curious variety of vine grown for years in the Botanic Garden at Grenoble, under the name of the double-flowered vine. The place of the flower is occupied by a large number of successive whorls of sepals disposed in regular order, and without any trace of the other portions of the flower. It is, in fact, more like a leaf-bud than a flower. The outermost whorls of this flower open at the time when the ordinary flowers of vines do; the second series are gradually produced, and expand about the time when the ovaries of the normal flowers begin to swell; a third series then gradually forms, and so on, until frost puts a stop to the growth. This malformation, it appears, is produced annually in certain varieties of vine, and may be perpetuated by cuttings.
The flower of the St. Valèry apple, already alluded to under the head of sepalody, might equally well be placed here. It is not very material whether the second whorl of organs be regarded as a repetition of the calyx or as a row of petals in the guise of sepals.
Engelmann[432] cites the following plants as occasionally presenting a repetition of the calyx, in most cases with a suppression of the other floral whorls:—Stachys lanata, Myosotis palustris, Veronica media, Aquilegia vulgaris, Nigella damascena, Campanula rapunculoides.
Pleiotaxy in the perianth.—Increase in the number of whorls in the perianth is common in lilies, narcissus, hyacinths, &c. It may be also met with occasionally among orchids. The lily of the valley (Convallaria maialis) seems also to be particularly subject to an increase in the number of parts of which its perianth consists, the augmentation being due partly to repetition or pleiotaxy, partly to the substitution of petaloid segments for stamens and pistils.[433]
In this place may also be mentioned the curious deviation from the ordinary structure occasionally met with in Lilium candidum, and known in English gardens as the double white lily. In this case there are no true flowers, but a large number of petal-like segments disposed in an irregular spiral manner at the extremity of the stem, some of the uppermost being occasionally verticillate.[434]