Chap. UI. OF THE RADICLE OP i'HASEOLUS. 165 



curvature extending for some little distance above 

 the apex. 



After the experience thus gained, the tips of six 

 almost dry radicles were once touched with the dry- 

 caustic on one side ; and after an interval of 10 m. 

 were allowed to enter water, which was kept at a 

 temperature of 65°-67° F. The result was that after 

 an interval of 8 h. a minute blackish speck could 

 just be distinguished on one side of the apex of five 

 of these radicles, all of which became curved towards 

 the opposite side — in two cases at about an angle 

 of 45° — in two other cases at nearly a rectangle — and 

 in the fifth case at above a rectangle, so that the apex 

 was a little hooked ; in this latter case the black mark 

 was rather larger than in the others. After 24 h. 

 from the application of the caustic, the curvature of 

 three of these radicles (including the hooked one) had 

 diminished ; in the fourth it remained the same, and 

 in the fifth it had increased, the tip being now hooked. 

 It has been said that after 8 h. black specks could 

 be seen on one side of the apex of five of the six 

 radicles ; on the sixth the speck, which was extremely 

 minute, was on the actual apex and therefore central ; 

 and this radicle alone did not become curved. It was 

 therefore again touched on one side with caustic, and 

 after 15 h. 30 m. was found curved from the perpen- 

 dicular and from the blackened side at an angle of 34°, 

 which increased in nine additional hours to 54°. 



It is therefore certain that the apex of the radicle 

 of this Phaseolus is extremely sensitive to caustic, 

 more so than that of the bean, though the latter is 

 far more sensitive to pressure. In the experiments 

 just given, the curvature from the slightly cauterised 

 side of the tip, extended along the radicle for a 

 length of nearly 10 mm.; whereas in the first sel 



