182 SENSITIVENESS OF THE APEX CHAP. ill. 



considerably curved towards the sieve ; and the absence of curva- 

 ture- in some of the others might perhaps be accounted for by 

 their not having grown very well. But it should be observed 

 that during the first 19 h. to 24 h. all grew well ; two of them 

 having increased 2 and 3 mm. in length in 11 h. ; five others 

 increased 5 to 8 mm. in 19 h. ; and two, which had been at first 

 4 and 6 mm. in length, increased in 24 h. to 15 and 20 mm. 



The tips of 10 radicles, which likewise grew well, were coated 

 with the grease for a length of only 1 mm., and now the result 

 was somewhat different ; for of these 4 curved themselves to 

 the sieve in from 21 h. to 24 h., whilst 6 did not do so. 

 Five of the latter were observed for an additional day, and now 

 all excepting one became curved to the sieve. 



The tips of 5 radicles were cauterised with nitrate of silver, 

 and about 1 mm. in length was thus destroyed. They were 

 observed for periods varying between 11 h. and 24 h., and wore 

 found to have grown well. One of them had curved until it 

 came into contact with the sieve ; another was curving towards 

 it ; whilst the remaining three were still vertically dependent. 

 Of 7 not cauterised radicles observed at the same time, all had 

 come into contact with the sieve. 



The tips of 11 radicles were protected by moistened gold- 

 beaters' skin, which adheres closely, for a length varying from 

 H to 2| mm. After 22 h. to 24 h., 6 of these radicles were 

 clearly bent towards or had come into contact with the sieve ; 

 2 were slightly curved in this direction, and 3 not at all. All 

 had grown well. Of 14 control specimens observed at the same 

 time, all excepting one had closely approached the sieve. It 

 appears from these cases that a cap of goldbeaters' skin checks, 

 though only to a slight degree, the bending of the radicles to 

 an adjoining damp surface. Whether an extremely thin sheet 

 of this substance when moistened allows moisture from the air 

 to pass through it, we do not know. One case indicated that 

 the caps were sometimes more efficient than appears from the 

 above results; for a radicle, which after 23 h. had only 

 slightly approached the sieve, had its cap (1^ mm. in length) 

 removed, and during the next 15 2 h. it curved itself abruptly 

 towards the source of moisture, the chief seat of curvature 

 being at a distance of 2 to 3 mm. from the apex. 



Vicia faba. The tips of 13 radicles were coated with the 

 grease for a length of 2 mm. ; and it should be remembered 

 that with these radicles the seat of chief curvature is about 



