238 



CIECUMNUTATION OF LEAVES. Chap. IV. 



day. On both days the leaf began to descend after 12 or 

 1 o'clock, and continued to do so all night, though to a 



very unequal distance on the 



Fig. 105. 



^4.5'pml". 



srj5am:i% 



■iO'40'p.mSff 



two occasions. We therefore 

 thought that the movement 

 was periodic; but on observ- 

 ing three other leaves during 

 several successive days and 

 nights, we found this to be an 

 error; and the case is given 

 merely as a caution. On the 

 third morning the above leaf 

 occupied almost exactly the 

 same position as on the first 

 morning ; and the tentacles 

 by this time had unfolded 

 sufSciently to project at right 

 angles to the blade or disc. 



The leaves as they grow 

 older generally sink more 

 and more downwards. The 

 movement of an oldish leaf, 

 the glands of which were 

 still secreting freely, was 

 traced for 24 h., during which 

 time it continued to sink a 

 little in a slightly zigzag Hne. 

 On the following morning, at 

 7 A.M., a drop of a solution 

 of carbonate of ammonia (2 

 gr. to 1 oz. of water) was 

 placed on the disc, and this 

 blackened the glands and in- 



Drosera rotundifolin : circumnutation 

 of young leaf, with fiiameat fixed 

 to back of blade, tr.iced from 9.13 

 A.M. June 7th to 8.30 a.m. June 

 9th. Figure here reduced to one- 

 half original scale. 



duced inflection of many of the tentacles. The weight of the 

 drop caused the leaf at first to sink a little ; but immediately 

 afterwards it began to rise in a somewhat zigzag course, and 

 continued to do so till 3 p.m. It then circumnutated about 

 the same spot on a very small scale for 21 h. ; and during the 

 next 21 h. it sank in a zigzag line to nearly the same level 

 which it had held when the ammonia was first administered. 

 By this time the tentacles had re-expanded, and the glands had 

 recovered their proper colour. We thus learn that an old lea* 



