. The origin of floral structures : through insect and other agencies. Plants; Flowers; Flowers. 156 THE STRUCTUEE OF FLOWERS. and never occurring without it, leaves no hereditary efEect as in the case of galls * and of the thickening of the tissues of some climbers after they have caught and clung to a foreign body, such as the petioles of Clematis,^ and the hooked peduncles of Uncaria (Fig. 46). In other cases the efEect has become hereditary, and may then be regarded as a specific character. These differences are well seen in the tendrils of Ampe- lopsis hederacea as compared â with those o
. The origin of floral structures : through insect and other agencies. Plants; Flowers; Flowers. 156 THE STRUCTUEE OF FLOWERS. and never occurring without it, leaves no hereditary efEect as in the case of galls * and of the thickening of the tissues of some climbers after they have caught and clung to a foreign body, such as the petioles of Clematis,^ and the hooked peduncles of Uncaria (Fig. 46). In other cases the efEect has become hereditary, and may then be regarded as a specific character. These differences are well seen in the tendrils of Ampe- lopsis hederacea as compared â with those of A. Veitchii. In the former there are no traces of the adhesive " pads " at the ter- minations of the slender hooked tips of the branching tendrils. Fig 46 -Climbing peduncle of Uncaria, Until contact with the surface of (ateTreubT' """"""^ ' '"^'""' * ^^'^ ^^^ Occurred. On the latter species, however, the pads are in course of development before any contact has takea place just as the aerial roots of Ivy begin to appear before contact. It is therefore reasonable to conclude that the effect of contact has become more or less hereditary in the latter Japanese species, though not in the American. These tendrils behave exactly like the clasping roots of Orchids, Ivy, etc., as well as the so-called " roots " of Lami- naria, Gutleria, etc. Indeed, the way in which subterra- nean root-hairs fix themselves to particles of the soil is by essentially the same method. The irritation caused by con- tact aided by moisture excites the cell-wall to grow out into protuberant processes, which enables it to adapt itself to the * I have examined a considerable nniuber of galls, and can quite corroborate M. Prillieux, who has shown how the normal tissues become hypertrophied {Ann. des Bei. Nat., sdr. 6, torn. ii. (1876), p. 113). t See Climbing Plants, fig. 1, p. 47, and fig. 4, p. Please note that these images are extracted
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Keywords: ., bookcentury1800, bookdecad, booksubjectflowers, booksubjectplants
