J 76 SENSITIVENESS OE THE APEX Chap. Ill 



though slight curvature from the square ; on the 23rd the tip 

 had curved up above the ho izon, and on the 24th was hooked 

 ■with the apex pointing almost to the zenith, as in Fig. 68. 



No. 6. Square attached on the 2ist; on the 22nd slightly 

 curved from the square; 23rd more curved; 25th consider- 

 ably curved; 27th all curvature lost, and the radicle was now 

 directed perpendicularly downwards. 



No. 7. Square attached on the 21st ; on the 22nd a trace of 

 curvature from the square, which increased next day, and on 

 the 24th amounted to a right angle. 



It is, therefore, manifest that the apex of the radicle 

 of the oak is highly sensitive to contact, and retains 

 its sensitiveness during several days. The movement 

 thus induced was, however, slower than in any of the 

 previous cases, with the exception of that of J^jscuIus. 

 As with the bean, the terminal growing part, after 

 bending, sometimes straightened itself through the 

 action of geotropism, although the object still remained 

 attached to the tip. 



The same remarkable experiment was next tried, 

 as in the case of the bean ; namely, little squares of 

 exactly the same size of the card-like sanded paper 

 and of very thin paper (the thicknesses of which have 

 been given under Vicia faha) were attached with 

 shellac on opposite sides (as accurately as could be 

 done) of the tips of 13 radicles, suspended in damp 

 air, at a temperature of 65°-66° F. The result was 

 striking, for 9 out of these 13 radicles became plainly, 

 and 1 very slightly, curved from the thick paper 

 towards the side bearing the thin paper. In two of 

 tliese cases the apex became completely hooked after 

 two days; in four cases the deflection from the per- 

 pendicular and from the side bearing the thick paper, 

 amounted in from two to four days to angles of 90°, 

 72°, 60°, and 49°, but in two other cases to only 18° 

 and 15°. It should, however, be stated that in the 



