Chap. XL GENEEAL SUMMARY. 271 



(•00024 mg.) is sufficient to excite a single tentacle 

 into movement. 



The nitrate of ammonia induces aggregation of the 

 protoplasm much less quickly than the carbonate, but 

 is more potent in causing inflection. A drop contain- 

 ing -2-rV-o of a grain ('027 mg.) placed on the disc acts 

 powerfully on all the exterior tentacles, which have 

 not themselves received any of the solution ; whereas a 

 drop with -^-g^'^j ^^ ^ grain caused only a few of these 

 tentacles to bend, but affected rather more plainly the 

 blade. A minute drop applied as before, and contain- 

 ing ^^l^^Q of a grain (-0025 mg.), caused the tentacle 

 bearing this gland to bend. By the immersion of 

 whole leaves, it was proved that the absorption by a 

 single gland of ^ .^ I'o o o ^^ ^ grain ('0000937 mg.) was 

 sufficient to set the same tentacle into movement. 



The phosphate of ammonia is much more powerful 

 than the nitrate. A drop containing ^Vt-o of a grain 

 (•0169 mg.) placed on the disc of a sensitive leaf 

 causes most of the exterior tentacles to be inflected, 

 as well as the blade of the leaf. A minute drop con- 

 taining ■ , ^ s'tj of a grain (-000423 mg.), applied for a 

 few seconds to a gland, acts, as shown by the move- 

 ment of the tentacle. When a leaf is immersed in 

 thirty minims (1-7748 ml.) of a solution of one part by 

 weight of the salt to 21,875,000 of water, the absorp- 

 tion by a gland of only the -rgTuVo-cro of a grain 

 (-00000328 mg.), that is, about the one-twenty-mil- 

 lionth of a grain, is sufficient to cause the tentacle 

 bearing this gland to bend to the centre of the 

 leaf. In this experiment, owing to the presence of 

 the water of crystallisation, less than the one-thirty- 

 millionth of a grain of the efficient elements could 

 have been absorbed. There is nothing remarkable in 

 such minute quantities being absorbed by the glands, 



