=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] [Illustration: FIG. 190.--Double white lily. Multiplication of perianth-segments and other changes.] =Pleiotaxy of the corolla.=--With reference to double flowers, it was remarked by Linne that polypetalous flowers were, as he said, multiplied, while monopetalous flowers were duplicated, or triplicated, as the case may be,[435] a statement that is true in the main, though it requires modification. In the case of polypetalous, or rather dialypetalous flowers, the petals may be very largely increased by multiplication, as in roses, anemones, pinks, &c. In the last-named genus the number is often so much increased that the calyx splits from the tension exercised on it by the increasing mass within. This multiplication may happen without any metamorphy or substitution of petals for stamens, though, in the majority of cases, it is associated with such a change. It is curious to observe in some of these flowers that the total number of parts is not greatly increased; thus, in some of the double-flowered _Leguminosae_, such as _Ulex europaeus_ and _Lotus corniculatus_, the petals are repeated once or twice, the stamens are petalodic, but reduced in number, while the carpels are usually entirely wanting. Thus, owing to the diminished number of parts in the inner whorls of the flower, these very double-looking blooms do not contain any greatly increased number of parts.[436] Flowers that, under ordinary circumstances, are gamopetalous, become, in some instances, multiplied by the formation of additional segments, just as in the case of polypetalous corollas; but in these cases the corollas become polypetalous, their petals do not cohere one with another. Among double flowers of this character may be mentioned _Campanula rotundifolia_, _Gardenia_ sp., _Nerium Oleander_, _Serissa_ sp., _Arbutus Unedo_, &c. The change is associated with petalody of the stamens and pistils.