OuAp. IIL 



OF THE EADICLE OF THE PEA. 



161 



these radicles are either less strongly acted on by 

 geotropism, or, what is more probable, are more sen- 

 sitive to contact. After a time geotropism always 

 pvcTailed, but its action was often delayed;' and iu 

 tliree instances there was a most curious struggle 

 between geotropism and the irritation caused by the 

 cards. Four of the 13 radicles were a little curved 

 downwards within 6 or 8 h., always reckoning from 

 the time when the squares were first attached, and 

 after 23 h. three of them pointed vertically down- 

 wards, and the fourth at an angle of 45° beneath the 

 horizon. These four radicles therefore did not seem 



Fig. 67. 



A. B. 



Pisum sativum: a radicle extended horizontally in damp air with a little 

 square of card affixed to the lower side of its tip, causing it to bend 

 upwards in opposition to geotropism. The deflection of the radicle 

 after 21 hours is shown at A, and of the same radicle after 45 hours at 

 B, now forming a loop. 



to have been at all affected by the attached squares. 

 Four others were not acted on by geotropism within 

 the first 6 or 8 h., but after 23 h. were much bowed 

 down. Two others remained almost horizontal for 

 23 h., but afterwards were acted on. So that in these 

 latter six cases the action of geotropism was much 

 delayed. The eleventh radicle was slightly curved 

 down after 8 h., but when looked at again after 23 h. 

 tlie terminal portion was curved upwards; if it had 



