N e w c o m b e . Thigmoti-opism of terrestrial roots. 71 



tively, 2 slightly negatively, and tlie otlier 7 grew straiglit. The 

 duration of one experiment was 6 lioiirs, and that'of tlie otliPv 

 13 liours. 



Collodion sacs, prepared as described on page G, were used 

 also to give pressure against the elongating zone. The results 

 here were no more condusive than in the precedmg tests. 



Better than the use of tongues of collodion and rubber tis- 

 sue for seciiring a continuous pressure on the elongating zone 

 was the employment of loops of rubber, collodion etc. suspended 

 at the lower end of a very light pendulum and pulling on the 

 root. These pendulums were usually made of iine tinned wire 

 and fine linen thread. The wire was lirst cut into lengths of 

 about 8 cm , and then beut double into a U- form. The thread 

 was in lengths of al.)out 30 cm. Tothe free ends of the bent 

 wire the loops of rubber, collodion etc. were fastened, and the 

 long thread was tied to the middle of the wire. This made a 

 penchilum in wliicli the wire corresponded to the bob. The pen- 

 dulum was suspended at any length desired by passing the 

 thread over a bar of wood raised above the jar of water in 

 wliich the experimental seedlings where placed. To insure the 

 retention of place by the pendulum, the thread bore acounter-weight 

 and the thin edge of wood over which the thread passed was cov- 

 ered by a rim of paraffin about 2 mm thick. In order to ad- 

 just the pull of the pendulum to the strengtli of the root, each 

 root was mounted on a separately movable Standard. 



In the first series of experiments with tliese pendulums, a 

 small rubber band 8 mm in diameter was grasped at the oppo- 

 site ends of its diameter by the ends of the bent wire. One 

 such rubber band was passed over the tip of each root and caus- 

 ed to pull gently against the lower part of the elongating zone, 

 by drawing the pendulum a little aside from its vertical position. 

 Every two or three hours, as the root advanced in growth, the 

 pendulum was lengthened so as to keep the rubber band against 

 the lower part of the elongating zone. The water was kept at 

 28 ° C. Seven seedlings of Raplianus sativus were used in this 

 experiment, and at the end of 5 hours, 2 roots had positive 

 curves, and 5 were straiglit. Four seedlings of Phaseolus vul- 

 garis for a period of 24 hours gave no response. Five seed- 

 lings of Zea mays (everta) during a period of 6 hours gave no 

 response. The number of söedlings employed in this test was 

 hardly enough for final judgment, but the result ■ indicates that 

 these roots are at least not strongly thigmotropic. 



Thinking that roots instead of continuous pressure may need 

 rubbing or percussion to show a response, another preparation 

 was made similar to the last, except that the jars were placed 

 on an unsteady wooden box to which was fastened a small Rabe 

 water-motor. A füll stream of water sent through the motor 

 caused it to rattle badly, and the rubber bands kept up a rapid 

 and gentle tapping against the roots. Ten seedlings of Zea mays 

 (everta) and 10 of Raphanus sativus were used in water kept 



