CHAP. III. OF THE RADICLE OF THE BEAN. 145 



of attachment. Bat in order to see the phenomenon 

 as well displayed as in the above described cases, it is 

 indispensable that the bits of card, &c., should be 

 made to adhere closely to one side of the conical 

 apex; that healthy radicles should be selected and 

 kept at not too high or too low a temperature, and 

 apparently that the trials should not be made in the 

 middle of the winter. 



In ten instances, radicles which had curved away 

 from a square of card or other object attached to their 

 tips, straightened themselves to a certain extent, or 

 even completely, in the course of from one to two days 

 from the time of attachment. This was more espe- 

 cially apt to occur when the curvature was slight. 

 But in one instance (No. 27) a radicle which in 9 h. 

 had been deflected about 90 from the perpendicular, 

 became quite straight in 24 h. frfjn the period of 

 attachment. With No. 26, the radicle was almost 

 straight in 48 h. We at first attributed the straighten- 

 ing process to the radicles becoming accustomed to a 

 slight stimulus, in the same manner as a tendril or 

 sensitive petiole becomes accustomed to a very light 

 loop of thread, and unbends itself though tho loop 

 remains still suspended ; but Sachs states * that radicles 

 of the bean placed horizontally in damp air after 

 curving downwards through geotropism, straighten 

 themselves a little by growth along their lower or 

 concave sides. Why this should occur is not clear ; 

 but perhaps it likewise occurred in the above ten 

 cases. There is another occasional movement which 

 must not be passed over : the tip of the radicle, for a 

 length of from 2 to 3 mm., was found in six instances, 



* l Arbeiten Bot. Instit., Wurzburg,' Heft iii. p. 456. 



