220 DROSERA ROTUNDIFOLIA. [Chap. XL 



The nitrate of ammonia induces aggr^ation of the pro- 

 toplasm much less quickly than the carbonate, but is more 

 potent in causing inflection. A drop containing Yitv 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 yVffv of a grain caused 

 only a few of these tentacles to bend, but affected rather 

 more plainly the blade. A minute drop applied as before, 

 and containing ^shsv 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 ^T^sjtv of a grain (.0000937 mg.) was sufficient to 

 set the same tentacle into movement. 



The phosphate of ammonia is much more powerful than 

 the nitrate. A Srop containing Wijs of a grain (.0169 mg.) 

 placed on the disc of a sensitive leaf causes most of the ex- 

 terior tentacles to be inflected, as well as the blade of the 

 leaf. A minute drop containing jzi^Tsv of a grain (.000423 

 mg.), applied for a few seconds to a gland, acts, as shown by 

 the movement of the tentacle. When a leaf is immersed in 

 thirty minims (1.7748 c.c.) of a solution of one part by 

 weight of the salt to 21,875,000 of water, the absorption by 

 a gland of only the Trr^vjnns of a grain (.00000328 mg.), 

 that is, a little more than the one-twenty-millionth 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, for all 

 physiologists admit that the salts of ammonia, which must 

 be brought in still smaller quantity by a single shower of 

 rain to the roots, are absorbed by them. Nor is it surprising 

 that Drosera should be enabled to profit by the absorption of 

 these salts, for yeast and other low fungoid forms flourish in 

 solutions of ammonia, if the other necessary elements are 

 present. But it is an astonishing fact, on which I will not 

 here again enlarge, that so inconceivably minute a quantity 

 as the one-twenty-millionth of a grain of phosphate of am- 

 monia should induce some change in a gland of Drosera, 

 sufficient to cause a motor impulse to be sent down the 



