iG8 SENSITIVENESS OF THE APEX Chap. Ill 



was nearly completed in 16 h. There can, therefore 

 be no doubt that the apex is higl.ly sensitive to slight 

 contact, and that the upper part of the radicle bends 

 away from the touching object. 



Gossypium herbaceum : Sensitiveness of the apex of the 

 Badicle. — Eadicles were experimented on in the same 

 manner as before, but they proved ill-fitted for our 

 purpose, as they soon became unhealthy when sus- 

 pended in damp air. Of 38 radicles thus suspended, 

 at temperatures varying from 66° to 69° P., with 

 squares of card attached to their tips, 9 were plainly 

 and 7 slightly or even doubtfully deflected from the 

 squares and from the perpendicular ; 22 not being 

 affected. We thought that perhaps the above tempera- 

 ture was not high enough, so 19 radicles with attached 

 squares, likewise suspended in damp air, were subjected 

 to a temperature of from 74° to 79° F., but not one of 

 them was acted on, and they soon became unhealthy. 

 Lastly, 19 radicles were suspended in water at a tem- 

 perature from 70° to 75° F., with bits of glass or 

 squares of the card attached to their tips by means of 

 Canada-balsam or asphalte, which adhered rather better 

 than shellac beneath the water. The radicles did not 

 keep healthy for long. The result was that 6 were 

 plainly and 2 doubtfully deflected from the attached 

 objects and the perpendicular ; 11 not being affected. 

 The evidence consequently is hardly conclusive, 

 though from the two sets of cases tried under a 

 moderate temperature, it is probable that the radicles 

 are sensitive to contact ; and would be more so under 

 favourable conditions. 



Fifteen radicles which had germinated in friable peat 

 were suspended vertically over water. Seven of them 

 served as controls, and they remained quite straight 

 during 24 h. The tips of the other eight radicles 



