It is generally supposed that the upper side of the tendril of _Passiflora_ is devoid of contractility. This is however not the case, for my experiments show that stimulation of the upper side also induces contraction and concavity of that side, though the actual movement is relatively feeble. _Experiment 109._--In order to subject the question to quantitative test I applied feeble stimulus of the same intensity on upper and lower side alternately. Successive stimuli were kept more or less uniform by employing the following device. I took a flat strip of wood 1 cm. in breadth, and coated 2 cm. of its length with shellac varnish mixed with fine emery powder. On drying the surface became rough, the flat surface was gently pressed against the area of the tendril to be stimulated, and quickly drawn so that the rough surface 2 cm.×1 cm. was rubbed against the tendril in each experiment. Stimulation, thus produced, induced a responsive movement of each side of the organ. The extent of the maximum movement was measured by the microscope micrometer. The following results were obtained with four different specimens. TABLE XXVII.--SHOWING THE RELATIVE INTENSITIES OF RESPONSES OF THE UPPER AND UNDER SIDE OF TENDRIL (_Passiflora_). +------------------------------------------------------------+ |Movement induced by | Movement induced by | B | | stimulation of under | stimulation of upper | Ratio ---. | | side, A. | side, B. | A | +----------------------+-------------------------------------+ |(1) 85 divisions | 14 divisions | 1/6 | |(2) 106 " | 15 " | 1/7 | |(3) 60 " | 8 " | 1/7 | |(4) 80 " | 10 " | 1/8 | +------------------------------------------------------------+ It will thus be seen that the upper side of the tendril is not totally inexcitable, its power of contraction being about one-seventh that of the under side. NEGATIVE CURVATURE OF THE TENDRIL. I shall now describe certain remarkable results which show that under certain definite conditions the tendril moves away from the stimulated side. I have explained, how in growing organs the effect of unilateral stimulus longitudinally transmitted, induces an expansion higher up on the same side to which the stimulus is applied, resulting in convexity and movement away from the stimulus (cf. Laws of Tropic Curvatures, p. 286). As the reaction of tendril is in no way different from that of growing organs in general, it occurred to me that it would be possible to induce in it a negative curvature by application of indirect unilateral stimulus.