Chap. VII. CARBONATE OF AMMONIA. 147 



safely assume that there were at least 140; and if so, each 

 gland could have received only the xaiVoo of a grain, or 

 •00048 mg. 



A weaker solution was then made of one part to 7000 of water, 

 and four leaves were immersed in it ; but I will give only one 

 case. A leaf was placed in ten minims of this solution ; after 

 1 hr. 37 m. the glands became somewhat darker, and the cells 

 beneath all of them now contained many spheres of aggregated 

 protoplasm. This leaf received -^-^^ of a grain, and bore 166 

 glands. Each gland could, therefore, have received only YY^iWs 

 of a grain ( • 000507 mg.) of the carbonate. 



Two other experiments are worth giving. A leaf was im- 

 mersed for 4 hrs. 15 m. in distilled water, and there was no 

 aggregation ; it was then placed for 1 hr. 15 m. in a little solu- 

 tion of one part to 5250 of water ; and this excited well-marked 

 aggregation and inflection. Another leaf, after having been 

 immersed for 21 hrs. 15 m. in distilled water, had its glands 

 blackened, but there was no aggregation in the cells beneath 

 them ; it was then left in six minims of the same solution, and 

 in 1 hr. there was much aggregation in many of the tentacles ; 

 in 2 hrs. all the tentacles (146 in number) were affected — the 

 aggregation extending down for a length equal to half or the 

 whole of .the glands. It is extremely improbable that these two 

 leaves would have undergone aggregation if they had been left 

 for a little longer in the water, namely for 1 hr. and 1 hr. 15 m., 

 during which time they were immersed in the solution ; for the 

 process of aggregation seems invariably to supervene slowly and 

 very gradually in water. 



Summary of the Results with Carhonafe of Ammonia. — 

 The roots absorb the solution, as shown by their changed 

 colour, and by the aggregation of the contents of their 

 cells. The vapour is absorbed by the glands ; these 

 are blackened, and the tentacles are inflected. The 

 glands of the disc, when excited by a half-minim drop 

 (•0296 ml.), containing -^^ of a grain (•0675 mg.), 

 transmit a motor impulse to the exterior tentacles, 

 causing them to bend inwards. A minute drop, con- 

 taining -xiiT-o of a grain (-00445 mg.), if held for a 

 few seconds in contact with a gland, soon causes the 

 tentacle bearing it to be inflected. If a leaf is left 



