[Illustration: FIG. 206.--Inflorescence of _Ranunculus acris_, with secondary peduncles lengthened.] In some of the double-flowered apples which have been previously alluded to, the flower-stalk is inordinately long when compared with the adjacent ones. Possibly in some of these cases the absence of the usual swelling of the upper part of the peduncle may be connected with its increased length. One of the most striking instances of lengthened flower-stalk occurred in an apple flower, wherein there was no swelling beneath the calyx, while the latter was represented by five perfect stalked leaves. =Elongation of the leaves.=--In the case of water plants this change keeps pace with the corresponding growth of the stem, _e.g._ _Ranunculus fluitans_, and in terrestrial plants there are varieties termed longifoliar, from the unusual length of the leaves. A similar lengthening occurs in the involucral leaves of _Umbelliferae_ and _Compositae_, changing very materially the general aspect of the inflorescence. Occasionally, also, the leaf-lobes of parsley (_Apium Petroselinum_) and other crested-leaved plants may be observed to lose their ordinary wavy form, and to be lengthened into flat riband-like segments, as shown in fig. 207. The only further illustrations that it is requisite to give of such changes in this place are those occurring in lobed or compounded leaves, which, from a lengthening of the midrib or central stalk, convert a digitate or palmate leaf into a pinnate one. In these instances the lobes or leaflets become separated one from another by a kind of apostasis. This change may be frequently seen in the horse-chestnut, particularly in the young shoots formed after the trees have been pruned or pollarded. In the adjoining cut the intermediate stages between a palmate or digitate leaf to a pinnate one may be seen. The specimens from which the drawing was made were taken from the same tree at the same time. [Illustration: FIG. 207.--Portion of leaf of parsley, showing the change from short wavy to long flat leaf-lobes.] In the white clover, _Trifolium repens_, a similar transition may often be observed, as also in some species of _Potentilla_.[514] =Elongation of the parts of the flower.=--The only circumstance that needs especial mention under this section is the great lengthening that sometimes takes place in the carpels, sometimes as a result of injury from insects or fungus, at other times without assignable cause. [Illustration: FIG. 208.--Leaves of horse-chestnut, _AEsculus_, showing passage from digitate to pinnate leaves.] In the case of inferior ovaries this lengthening is, perhaps, even more common, as in _Umbelliferae_, _Compositae_, &c. The common groundsel (_Senecio vulgaris_) is especially liable to this form of enlargement of the pistil, either in association with a leafy condition of the pappus or without any such change.