The origin of floral structures through insect and other agencies . tof external stimuli. Sparviannia, it may be added, exhibitsthree kinds of movement, Sleep in the calyx and corolla,ineclianical irritability in the stamens, and an elevation of thepeduncle. (See Heckel, , p. 210.) If this position begranted we have at least a woi-king hypothesis for thepresent theory of the origin of floral structures. Formation of Tissues due to Irritability.—Apart fromthe preceding theoretical supposition, there may be fre-quently witnessed an actual formation of tissues of variouskinds, through h
The origin of floral structures through insect and other agencies . tof external stimuli. Sparviannia, it may be added, exhibitsthree kinds of movement, Sleep in the calyx and corolla,ineclianical irritability in the stamens, and an elevation of thepeduncle. (See Heckel, , p. 210.) If this position begranted we have at least a woi-king hypothesis for thepresent theory of the origin of floral structures. Formation of Tissues due to Irritability.—Apart fromthe preceding theoretical supposition, there may be fre-quently witnessed an actual formation of tissues of variouskinds, through hypertrophy on the one hand, often coupledwith atrophy on the other, and entirely brought about byphysical or mecbanical irritations. Cell-division is thus setup, a result which would not have occurred had not theexternal stimulus been applied. It is an important fact to notice, that in some cases theabnormal growth, though immediately following the stimulus,* See Jl. Roy. Micr. Soc, 1886, p. 287; and Bull. Soc. Bot. Fr., 21, p. 65. 156 THE STRUCTURE OF and never occurring without it, leaves no hereditary effect asin the case of galls * and of the thickening of the tissues ofsome climbers after they have caught and clung to a foreignbody, such as the petioles of Clematis,^ and the hookedpeduncles of Uncaria (Fig. 46). In other cases the effect has become hei-editary, and maythen be regarded as a specificcharacter. These differences arewell seen in the tendrils of Ampe-lopsis hederacea as comparedwith those of A. Veitchii. Inthe former there are no traces ofthe adhesive pads at the ter-minations of the slender hookedtips of the branching tendrils. Fig. 46.—Climbing peduncle of Uncaria, Until Contact with the surface ofthickenej after catching a sunport „ ii i, j /~i ji (after Treub). ^ vfull nas Occurred. (Jn the latter species, however, the padsare in course of development before any contact has takenplace just as the aerial roots of Ivy begin to appear beforecon
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectfertili, bookyear1888
