172 SENSITIVENESS OF THE APEX CHAF. III. 



and a third very slightly from the perpendicular and 

 from the cauterised side. 



jEsculus hippocastanum : Sensitiveness of the apex of 

 the Radicle. Bits of glass and squares of card were 

 affixed with shellac or gum-water to the tips of 12 

 radicles of the horse-chestnut ; and when these objects 

 fell off, they were refixed ; but not in a single instance 

 was any curvature thus caused. These massive 

 radicles, one of which was above 2 inches in length 

 and 3 inch in diameter at its base, seemed insensible 

 to so slight a stimulus as any small attached object. 

 Nevertheless, when the apex encountered an obstacle 

 in its downward course, the growing part became so 

 uniformly and symmetrically curved, that its appear- 

 ance indicated not mere mechanical bending, but 

 increased growth along the whole convex side, due to 

 the irritation of the apex. 



That this is the correct view may be inferred from 

 the effects of the more powerful stimulus of caustic. 

 The bending from the cauterised side occurred much 

 slower than in the previously described species, and it 

 will perhaps be worth while to give our trials in 

 detail. 



The seeds germinated in sawdust, and one side of the tips of 

 the radicles were slightly rubbed once with dry nitrate of silver ; 

 and after a few minutes were allowed to dip into water. They 

 were subjected to a rather varying temperature, generally 

 between 52 and 58 F. A few cases have not been thought 

 worth recording, in which the whole tip was blackened, or in 

 which the seedling soon became unhealthy. 



(1.) The radicle was slightly deflected from the cauterised 

 side in one day (i.e. 24 h.) ; in three days it stood at 60 from 

 the perpendicular ; in four days at 90 ; on the fifth day it was 

 curved up about 40 above the horizon ; so that it had passed 

 through an angle of 130 in the five days, and this was the 

 greatest amount of curvature observed. 



(2.) In two days radicle slightly deflected ; after seven days 



