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Show 336 IJAR WINIAN A. movement may be plainly seen; indeed, we have seen. a quarter-circuit in a Passijlora sicyo~des. ac?omplis~ed in less than a minute, and the half-C!rcmt m ten mmutes · but the other half (for a reason alluded to in the next' paragraph) takes a m?-ch longer time. Then, as to the coiling upon contact, in the case first noticed in this country/ in· the ·year 1858, which Mr. Darwin menti0ns as having led him into this investigation, the tendril of Sicyos was seen to coil within half a minute after a stroke with the hand, and to make a full turn or more within the next minute; furnishing ocular evidence that tendrils grasp and coil in virtue of sensitiveness to contact, and, one would suppose, negativing Sachs's recent hypothesis that all these movements are owing "to rapid growth on the side opposite to that which becomes concave "-a view to which :Mr. Darwin objects, but not so strongly as he might. The tendril of this sort, on striking some fitting object, quickly curls round and firmly grasps it; then after some hours, one side shortening or remaining ~hort in proportion to the other, it coils into a spire, dragging the stem up to its support, and e~abling the next tendril above to secure a read1er hold. In revolving tendrils perhaps the most wonderful adaptation is that by which they avoid attachment to, or windinO' themselves upon, the ascending summit of the stem fuat bears them. This they would inevitably· do if they continued tl;leir sweep horizontally. But t [A. Gray, in "Proceedings of the American Aradem~ of Arts and Sciences," vol. iv., p. 98; and American Journal of Scwnce and tlte Arts, March, 1859, p. 278.] INSECTIVOROUS ANIJ CLIMBING PLANTS. 337 when in its course it nears the parent stem the tendril . moves slowly, as if to gather strength, then stiffens and rises into an erect position para]lel with it, and so passes by the dangerous point; after which it comes rapidly down to the horizontal position, in which it moves until it again approaches and aO'ai~ avoids the impending obstacle. · 0 Climbing plants are distributed throughout almost all the natural orders. In some orders climbing is the rule, in most it is the exception, occurring only in certain genera. The tendency of stems to move in circuits-upon which climbing more commonly depends, and out of which it is conceived to have been educed-is manifested incipiently by many a plant which does not climb. Of those that do there are all degrees, from the feeblest to the most efficient, · from those which have no special adaptation to those which have exquisitely-endowed special organs for climbing. The co~clusion reached is, that the power "is inherent, though undeveloped, in almost every plant;" "that climbing plants have utilized and per- · fected a widely-distributed and incipient capacity, which, as far as we can see, is of no service to ordinary plants." Inherent powers and incipient manifestations, use- less to their possessors but useful to their successorsthis, doubtless, is according to the order of Nature ; but it seems to need something more than natural selection to account for it. |
