150 SENSITIVENESS OF THE APEX CHAP. III. 



ture followed. Secondly, thin slices were . cut with a 

 razor obliquely off the tips of three radicles similarly 

 suspended; and after 44 h. two were found plainly 

 bent from the sliced surface ; and the third, the whole 

 apex of which had been cut off obliquely by accident, 

 was curled upwards over the bean, but it was not 

 clearly ascertained whether the curvature had been at 

 first directed from the cut surface. These results led 

 us to pursue the experiment, and 18 radicles, which 

 had grown vertically downwards in damp air, had one 

 side of their conical tips sliced off with a razor. The 

 tips were allowed just to enter the water in the jars, 

 and they were exposed to a temperature 14-16 C. 

 (57-61 F.). The observations were made at dif- 

 ferent times. Three were examined 12 h. after being 

 sliced, and were all slightly curved from the cut 

 surface; and the curvature increased considerably after 

 an additional 12 h. Eight were examined after 19 h. ; 

 four after 22 h. 30 m. ; and three after 25 h. The 

 final result was that out of the 18 radicles thus tried, 

 13 were plainly bent from the cut surface after the 

 above intervals of time ; and one other became so 

 after an additional interval of 13 h. 30 m. So that 

 only 4 out of the 18 radicles were not acted on. To 

 these 18 cases the 3 previously mentioned ones should 

 be added. It may, therefore, be concluded that a thin 

 slice removed by a razor from one side of the conical 

 apex of the radicle causes irritation, like that from an 

 attached object, and induces curvature from the injured 

 surface. 



Lastly, dry caustic (nitrate of silver) was employed 

 to irritate one side of the apex. If one side of the 

 apex or of the whole terminal growing part of a 

 radicle, is by any means killed or badly injured, the 

 other side continues to grow ; and this causes the part 



