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.
Fig. 208.—Leaves of horse-chestnut, Æsculus, showing passage from digitate to pinnate leaves.
In the case of inferior ovaries this lengthening is, perhaps, even more common, as in Umbelliferæ, Compositæ, &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.
Elongation of the thalamus, placenta, &c.—In some plants, as in Magnolia or Myosurus, the thalamus becomes much elongated, and bears the carpels disposed spirally around it. A similar lengthening occurs in malformed flowers, usually in association with a similar change in the lower or outer part of the flower, by virtue of which the whorls become separated from each other (Apostasis). Elongation and protrusion of the placenta have been already alluded to at p. 119, and also at p. 125. In some of these cases the elongated placenta has taken the form of a leaf-bearing shoot.[515]