244 MOVEMENT IN PLANTS. 



335. Tendrils irresponsive to Stimulation with Gelatine. 



Make a 15 per cent, solution of gelatine in hot water in a test- 

 tube, and dip into it two glass rods, or pieces of glass tubing, so as 

 to coat thickly a length of about 5 cm. of each. When the gelatine 

 sets, touch the convex side of a tendril with one rod so as to hold 

 the tendril (the gelatine being slightly sticky), and with the other 

 rod rub the lower side in the reacting region. No curvature takes 

 place evidently the tendril cannot distinguish gelatine from a 

 liquid. Now rub with the uncoated part of the rod ; curvature 

 takes place. 



336. Growth in Upper and Lower Sides of Tendril. 



Carefully mark, in each case with two ink dots or transverse lines, 

 a zone on (1) the convex, (2) the concave side of a slightly hooked 

 young tendril, and measure the distance between the marks in each 

 case, after allowing the tendril to straighten should the act of 

 marking cause curvature. Stimulate the tendril strongly, and note 

 that the curvature is due to the great growth in length of the upper 

 side ; the marks on the lower side come a little closer together. 

 The neutral line lies below the middle (axial) line of the tendril, 

 and is close to the concave side. The whole movement following 

 stimulation is complex, since the curvature is not effected by simple 

 contraction of the stimulated side, but by acceleration of growth, 

 which is greatest at the spot on the convex side directly opposite 

 that on the concave side where the stimulus has been applied. 

 Perception, transmission, and reaction follow each other much more 

 rapidly than in any of the tropistic movements studied so far. 



Soon after the completion of the curvature, growth ceases, and 

 then the tendril begins to straighten ; the convex side remains 

 unaltered, while growth occurs on the concave side less vigorously 

 than that which took place on the convex side during curvature, but 

 still showing a marked acceleration of growth as compared with 

 that of an unstimulated tendril. This straightening is evident!}' 

 a case of autotropism. 



337. How the Tendril clasps its Support. So far 



we have been studying the effects of a temporary contact 

 stimulus. When the tendril rubs against a fixed support 

 it curves, and thus new parts come into contact with 

 the support. 



(a) If the support is of the right thickness, tension 

 arises which exerts pressure on the support to observe 

 this, use a roll of paper as a support. This pressure does 

 not act as a stimulus, but the reverse curvature which 

 appears causes the loosening of the coil, and there is set up 



