Chap. VII.] PHOSPHATE OF AMMONIA. 135 



(2) to (8) These leaves, after 2 hrs. 40 m., had respectively 42, 

 12, 9, 8,2, 1, and tentacles inflected, which all re-expanded within 

 24 hrs., and most of them within a much shorter time. 



When the two lots of eight leaves in the solution and in the 

 water were compared after the lapse of 24 hrs., they undoubtedly 

 differed much in apjiearance. The few tentacles on the leaves in 

 water which were inflected had after this interval re-expanded, with 

 the exception of one leaf; and this presented the very unusual case 

 of the blade being somewhat inflected, though in a degree hardly 

 approaching that of the two leaves in the solution. Of these latter 

 leaves, No. 1 had almost all its tentacles, together with its blade, 

 inflected after an immersion of 2 hrs. 30 m. Leaves No. 2 and 3 

 were affected at a much slower rate; but after from 24 hrs. to 48 

 hrs. almost all their tentacles were closely inflected, and the blade 

 of one quite doubled up. We must therefore admit, incredible as 

 the fact may at first appear, that this extremely weak solution 

 acted on the most sensitive leaves ; each of which received only the 

 go^flj of a grain (.00081 mg.) of the phosphate. Now, leaf No. 3 

 bore 178 tentacles, and, subtracting the three which were not in- 

 flected, each gland could have absorbed only the uoi ^ oooo o^ * 

 grain, or .00000403 mg. Leaf No. 1, which was strongly acted on 

 within 2 hrs. 30 m., and had all its outer tentacles, except thirteen, 

 inflected within 6 hrs. 30 m., bore 260 tentacles; and, on the same 

 principle as before, each gland could have absorbed only ^^^-^t!VJ^s 

 of a grain, or .00000328 mg. ; and this excessively minute amount 

 sufficed to cause all the tentacles bearing these glands to be greatly 

 inflected. The blade was also inflected. 



Summary of the Results with Phosphate of Ammonia. 

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

 (.0296 c.c), containing v^rs of a grain (.0169 mg.) of this 

 salt, transmit a motor impulse to the exterior tentacles, caus- 

 ing them to bend inwards. A minute drop, containing 

 nJgaa of a grain (.000423 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 a shorter time, in a solution so weak that 

 each gland can absorb only the h t 8^0 jo t of a grain 

 (.00000328 mg.^, this is enough to excite the tentacle into 

 movement, so that it becomes closely inflected, as does some- 

 times the glade. In the general summary to this chapter a 

 few remarks will be added, showing that the efficiency of 

 such extremely minute doses is not so incredible as it must 

 at first appear. 



F!iilphate of Ammonia. The few trials made with this and the 

 following five salts of ammonia were undertaken merely to ascer- 



