The class of cases coming under this head are sufficiently indicated by the name. There are many instances of this phenomenon occurring under different conditions, which, though unusual, can hardly be called abnormal, such, for instance, as the great lengthening of roots in their search for water, the excessive elongation that takes place in plants when grown at a distance from the light, in their endeavour to attain to which they become, as gardeners phrase it, "drawn." A similar result is brought about in forests or plantations, where long spars are required, by allowing the trees to grow very close to each other, so as to prevent the lateral extension of the branches. When plants grow in running water their roots, stems, and sometimes their leaves, become excessively elongated, as in _Ranunculus fluitans_, the flower-stalks of _Valisneria spiralis_, &c. These are cases of variation rather than of malformation, but are none the less curious, or sometimes perplexing; thus, Lapeyrouse described, in his 'Supplement a la flore des Pyrenees,' p. 27, under the name _Potamogeton bifolium_, a plant which Mr. Bentham subsequently discovered to be nothing but a flowerless variety of _Vicia Faba_ distorted by its growth in water.[510] =Elongation of the root.=--This, as already remarked, is more often a variation than a malformation, and is usually due to the presence of water at a distance necessitating growth at the extremities of the root, or to the presence of some obstacle, such as a stone, to avoid which the root elongates till it has passed the obstruction. Occasionally in Crocus corms some of the fibrils may be met with much lengthened and thickened, and invested with a fleshy sheath. It is not certain, however, that these structures are roots; possibly, nay probably, they may be processes from the stem thrust downwards into the soil, similar to the formations already described in the tulip (p. 85, fig. 39). =Elongation of the inflorescence.=--Under this heading it is necessary to consider lengthening of the common rachis in the case of an aggregate inflorescence, and lengthening of the individual flower-stalks, whether they be solitary or portions of a multiple inflorescence. The two phenomena may occur together, but they are quite as often independent one of the other. Thus, among _Umbelliferae_ the umbels are occasionally met with supported on unusually long stalks, while the pedicels of the individual flowers may or not be increased in length; so also with some of the Composites, or the heads of flowers of some _Leguminosae_, _Trifolium repens_, &c. &c. Another illustration of the sort is that recorded by M. Fournier, wherein the usually umbellate inflorescence of _Pelargonium_ was, through the lengthening of the main stalk, transformed into a raceme. Among Composites a similar change may sometimes be met with.