Chap. HI. OF THE KADICLE TO MOIST AIR. 183 



4 or 5 mm. from the apex. Four of them were examined after 

 22 h., three after 26 h., and six after 36 h., and none had 

 been attracted towards the damp lower surface of the sieve. 

 In another trial 7 radicles were similarly treated, and 5 of tliem 

 still pointed perpendicularly downwards after 11 h., whilst 



2 were a little curved towards the sieve; by an accident thty 

 were not subsequently observed. In both these trials the 

 radicles grew well ; 7 of them, which were at fii'st from i to 

 11 mm. in length, were after 11 h. between 7 and 16 mm. ; 



3 which were at first from 6 to 8 mm. after 26 h. were 115 

 to 18 mm. in length; and lastly, 4 radicles which were at first 



5 to 8 mm. after 46 h. were 18 to 23 mm. in length. The 

 control or ungreased radicles were not invariably attracted 

 towards the bottom of the sieve. But on one occasion 12 oiit of 

 13, which were observed for periods between 22 h. and 36 h., 

 were thus attracted. On two other occasions taken together, 

 38 out of 40 were similarly attracted. On another occasion 

 only 7 out of 14 behaved in this manner, but after two more 

 days the proportion of the curved increased to 17 out of 23. 

 On a last occasion only 11 out of 20 were thus attracted. If 

 we add up these numbers, we find that 78 out of 96 of the 

 control specimens curved themselves towards the bottom of the 

 sieve. Of the specimens with greased tips, 2 alone out of the 

 20 (but 7 of these were not observed for a sufficiently long 

 time) thus curved themselves. We can, therefore, hardly doubt 

 that the tip for a length of 2 mm. is the part which is sensitive 

 to a moist atmosphere, and causes the upper part to bend 

 towards its source. 



The tips of 15 radicles were cauterised with nitrate of silver, 

 and they grew as well as those above described with greased 

 tips. After an interval of 24 h., 9 of them were not at all 

 curved towards the bottom of the sieve ; 2 were curved towards 

 it at angles of 20° and 12° from their former vertical position, 

 and 4 had come into close contact with it. Thus the destruc- 

 tion of the tip for a length of about 1 mm. prevented the curva- 

 ture of the greater number of these radicles to the adjoining 

 damp surface. Of 24 control specimens, 23 were bent to the 

 sieve, and on a second occasion 15 out of 16 were similarly 

 curved in a greater or less degi'ee. These control trials are 

 included in those given in the foregoing paragraph. 



Avena sativa. — The tips of 13 radicles, which projected 

 between 2 and 4 mm. from the bottom of the sieve, many of 

 13 



