132 SENSITIVEXESS OF THE APEX Chap. lH 



liereafter see, Sachs discovered that the radicle a little 

 above the apex is sensitive, and bends like a tendril 

 towards the touching object. But when one side of the 

 apex is pressed by any object, the growing part bends 

 away from the object; and this seems a beautiful 

 adaptation for avoiding obstacles in the soil, and, as 

 we shall see, for following the lines of least resistance. 

 Many organs, when touched, bend in one fixed direc- 

 tion, such as the stamens of Berberis, the lobes of 

 Dionsea, &c. ; and many organs, such as tendrils, whe- 

 ther modified leaves or flower-peduncles, and some few 

 stems, bend towards a touching object ; but no case, 

 we believe, is known of an organ bending away from 

 a touching object. 



Sensitiveness of the Aj>ex of the Badicle of Vicia faha. 

 — Common beans, after being soakeid in water for 24 h., 

 were pinned with the hilum downwards (in the manner 

 followed by Sachs), inside the cork lids of glass-vessels, 

 which were half filled with water; the sides and the 

 cork were well moistened, and light was excluded. 

 As soon as the beans had protruded radicles, some to a 

 length of less than a tenth of an inch, and others to 

 a length of several tenths, little squares or oblongs of 

 card were affixed to the short sloping sides of their 

 conical tips. The squares therefore adhered obliquely 

 with reference to the longitudinal axis of the radicle ; 

 and this is a very necessary precaution, for if the bits 

 of card accidentally became displaced, or were drawn 

 by the viscid matter employed, so as to adhere parallel 

 to the side of the radicle, although only a little way 

 above the conical apex, the radicle did not bend in 

 the peculiar manner which we are here considering. 

 Squares of about the ^^jth of an inch (i.e. about 1 J mm.), 

 or oblong bits of nearly the same size, were found to 



