CH. V] 



STIPA. 



103 



(131) Stipa pennata. 



The awn of Stipa pennata is, as previously explained, 

 extremely hygroscopic, untwisting when wetted, and 

 twisting again when dried. To observe its movements it 

 must be fitted up as shown in fig. 20. The awn S is 



I 



Fio. 20, Exp. 131. 



lashed with fine wire to a strong straight wire above, and 

 below to a hooked wire W: the latter, W, is fixed into the 

 cork G, which is attached underneath the stout paper 

 or cardboard P: in the middle of P is a hole through 

 which the straight wire passes, bearing at right angles the 

 index I. On the upper surface of P a circle is marked, 

 and is divided into degrees which may be 2 or 3 mm. in 

 width. When the Stipa-awn is dipped in water the 

 index moves round the clock-face in one direction, which 



