Chap. VII.] PHOSPHATE OF AMMONIA. 125 



perhaps produces a slight eflFect; but we must bear in mind that 

 occasionally water causes as great an amount of inflection as oc- 

 curred in this last experiment. 



.' . 



Summary of the Results with Nitrate of Ammonia. The 



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

 (.0296 C.C.), containing yjVjr of a grain of the nitrate (.027 

 mg.), transmit a motor impulse to the exterior tentacles, 

 causing them to bend inwards. A minute drop, containing 

 trkvv of a grain (.00225 mg.), if held for a few seconds in 

 contact with a gland, causes the tentacle bearing this gland 

 to be inflected. If a leaf is left immersed for a few hours, 

 and sometimes for only a few minutes, in a solution of such 

 strength that each gland can absorb only the tWsTs of a 

 grain (.0000937 mg.), this small amount is enough to excite 

 each tentacle into movement, and it becomes closely in- 

 flected. 



PHOSPHATE OP AMMONTA. 



This salt is more powerful than the nitrate, even in a 

 greater degree than the nitrate is more powerful than the 

 carbonate. This is shown by weaker solutions of the phos- 

 phate acting when dropped on the discs, or applied to the 

 glands of the exterior tentacles, or when leaves are im- 

 mersed. The difference in the power of these three salts, as 

 tried in three different ways, supports the results presently 

 to be given, which are so surprising that their credibility re- 

 quires every kind of support. In 1872 I experimented on 

 twelve immersed leaves, giving each only ten minims of a 

 solution : but this was a bad method, for so small a quantity 

 hardly covered them. None of these Qxi)eriments will, there- 

 fore, be given, though they indicate that excessively minute 

 doses are efficient. When I read over my notes, in 1873, I 

 entirely disbelieved them, and determined to make another 

 set of experiments with scrupulous care, on the same plan as 

 those made with the nitrate; namely by placing leaves in 

 watch-glasses, and pouring over each thirty minims of the 

 solution under trial, treating at the same time and in the 

 same manner other leaves with the distilled water used in 

 making the solutions. During 1873, seventy-one leaves were 

 thus tried in solutions of various strengths, and the same 



