CHAP. III. OF THE KADICLE OF TKOP^EOLUM. 167 



respect to the eighth which remained quite straight, 

 too thick a slice had been accidentally removed, so 

 that it hardly formed a real exception to the general 

 result. When the seven radicles were looked at 

 again, after an interval of 23 h. from the time of 

 slicing, two had become distorted ; four were deflected 

 at an angle of about 70 from the perpendicular and 

 from the cut surface ; and one was deflected at nearly 

 90, so that it projected almost horizontally, but with 

 the extreme tip now beginning to bend downwards 

 through the action of geotropism. It is therefore 

 manifest that a thin slice cut off one side of the conical 

 apex, causes the upper growing part of the radicle of 

 this Phaseolus to bend, through the transmitted effects 

 of the irritation, away from the sliced surface. 



Trop&olum majus: Sensitiveness of the apex of the 

 Radicle to contact. Little squares of card were attached 

 with shellac to one side of the tips of 19 radicles, some 

 of which were subjected to 78 F., and others to a 

 much lower temperature. Only 3 became plainly 

 curved from the squares, 5 slightly, 4 doubtfully, 

 and 7 not at all. These seeds were, as we believed, 

 old, so we procured a fresh lot, and now the results 

 were widely different. Twenty-three were tried in 

 the same manner ; five of the squares produced no 

 effect, but three of these cases were no real exceptions, 

 for in two of them the squares had slipped and were 

 parallel to the apex, and in the third the shellac was 

 in excess and had spread equally all round the apex. 

 One radicle was deflected only slightly from the 

 perpendicular and from the card ; whilst seventeen 

 were plainly deflected. The angles in several of these 

 latter cases varied between 40 and 65 from the 

 perpendicular ; and in two of them it amounted after 

 15 h. or 16 h. to about 90. In one instance a loop 



