Cuar. XI] GENERAL SUMMARY. 219 
The phosphate of ammonia is much more powerful than 
the nitrate. A drop containing 544, 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 ysz/gqq 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 (17748 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 ygr¢ooon Of a grain (*00000328 mg.), 
that is, a little more than the one-twenty-millionth of a 
grain, is suflicient 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 
ammonia should induce some change in a gland of Drosera, 
sufficient to cause a motor impulse to be sent down the 
whole length of the tentacle; this impulse exciting move- 
ment often through an angle of above 180°. I know not 
whether to be most astonished at this fact, or that the 
pressure of a minute bit of hair, supported by the dense 
secretion, should quickly cause conspicuous movement. 
Moreover, this extreme sensitiveness, exceeding that of the 
most delicate part of the human body, as well as the power 
of transmitting various impulses from one part of the leaf to 
another, have been acquired without the intervention of any 
nervous system, 
As few plants are at present known to possess glands 
specially adapted for absorption, it seemed worth while to 
try the effects on Drosera of various other salts, besides 
those of ammonia, and of various acids. Their action, as 
described in the eighth chapter, does not correspond at all 
