272 DROSERA ROTUNDIFOLIA. Cuar. XL 
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 pre- 
sent. 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 movement 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 transmit- 
ting 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 strictly with their chemical affinities, 
as inferred from the classification commonly followed. 
The nature of the base is far more influential than 
that of the acid ; and this is known to hold good with 
animals. For instance, nine salts of sodium all caused 
we.l-marked inflection, and none of them were poison- 
ous in smal] doses; whereas seven of the nine corre 
