160 SENSITIVENESS OF THE APEX CHAP. III. 



of card attached to their tips. Firstly, 13 peas, most 

 of them having very short and young radicles, were 

 placed in an ice-box, in which the temperature rose 

 during three days from 44 to 47 F. They grew slowly, 

 but 10 out of the 13 became in the course of the three 

 days very slightly curved from the squares ; the other 

 3 were not aifected ; so that this temperature was too 

 low for any high degree of sensitiveness or for much 

 movement. Jars with 13 other radicles were next 

 placed on a chimney-piece, where they were subjected 

 to a temperature of between 68 and 72 F., and 

 after 24 h., 4 were conspicuously curved from the 

 cards, 2 slightly, and 7 not at all ; so that this tem- 

 perature was rather too high. Lastly, 12 radicles 

 were subjected to a temperature varying between 

 72 and 85 F., and none of them were in the least 

 affected by the squares. The above several trials, 

 especially the first recorded one, indicate that the 

 most favourable temperature for the sensitiveness of 

 the radicle of the pea is about 60 F. 



The tips of 6 vertically dependent radicles were 

 touched once with dry caustic, in the manner described 

 under Vicia fdba. After 24 h. four of them were bent 

 from the side bearing a minute black mark ; and the 

 curvature increased in one case after 38 h., and in 

 another case after 48 h., until the terminal part pro- 

 jected almost horizontally. The two remaining ra- 

 dicles were not affected. 



With radicles of the bean, when extended horizontally 

 in damp air, geotropism always conquered the effects 

 of the irritation caused by squares of card attached to 

 the lower sides of their tips. A similar experiment 

 was tried on 13 radicles of.the pea; the squares being 

 attached with shellac, and the temperature between 

 58-60 F. The result 'was somewhat different ; for 



