CH. VIIl] DROSERA. 193 



ever proved', when sufficient care is taken to prevent the 

 vibration of the room reaching the leaf, that a smooth 

 particle of glass which is comparatively heavy may rest 

 on the gland without producing movement of the 

 tentacle. 



(240) Drosera: inflection caused by dilute solutions^. 



Very dilute solutions of ammonium phosphate cause 

 inflection. Prepare with good distilled water a solution 

 of ammonium phosphate in the proportion of 1 to 50,000 

 (2 centigrams to a liter). Fill 10 watch-glasses with the 

 solution and 10 others with the distilled water used in 

 making the solution. In each glass place a healthy leaf, 

 and examine them after an hour, when the phosphate 

 leaves should show much inflection, whereas only a few 

 isolated tentacles in the control leaves ought to have 

 moved. 



(241) Drosera: asymmetrical inflection. 



If a particle of raw meat, or preferably a minute frag- 

 ment of calcium phosphate, is placed in the middle of a 

 leaf the exterior tentacles all bend towards the centre. If 

 however the object is excentrically placed, e.g. half way 

 between the centre and circumference of the disc of the 

 leaf, the tentacles no longer bend symmetrically towards 

 the centre, but are plainly directed towards the phos- 

 phate'. 



' Untersuchungen aus d. Bot. Institut zu Tubingen, i. p. 513. 



^ Insectivorous Plants, p. 153. 



' See Insectivorous Plants, Eig. 10, p. 244. 



D. A. 13 



