140 DROSERA ROTUNDIFOLIA. (Cuar. VIL. 
drops applied to the glands of the outer tentacles, and by the 
immersion of whole leaves; and it was found by these three 
methods that the nitrate was more powerful than the car- 
bonate, and the phosphate much more powerful than the 
nitrate; this result being intelligible from the difference in 
the amount of nitrogen in the first two salts, and from the 
presence of phosphorus in the third. It may aid the reader’s 
faith to turn to the experiments with a solution of one grain 
of the phosphate to 1000 oz. of water, and he will there find 
decisive evidence that the one-four-millionth of a grain is 
sufficient to cause the inflection of a single tentacle. There 
is, therefore, nothing very improbable in the fifth of this 
weight, or the one-twenty-millionth of a grain, acting on the 
tentacle of a highly sensitive leaf. Again, two of the leaves 
in the solution of one grain to 3000 oz., and three of the 
leaves in the solution of one grain to 5000 oz., were affected, 
not only far more than the leaves tried at the same time in 
water, but incomparably more than any five leaves which 
can be picked out of the 173 observed by me at different 
times in water. 
There is nothing remarkable in the mere fact of the one- 
twenty-millionth of a grain of the phosphate, dissolved in 
about two million times its weight of water, being absorbed 
by a gland. All physiologists admit that the roots of plants 
absorb the salts of ammonia brought to them by the rain; 
and fourteen gallons of rain-water contain* a grain of 
ammonia, therefore only a little more than twice as much as 
in the weakest solution employed by me. The fact which 
appears truly wonderful is, that the one-twenty-millionth of 
a grain of the phosphate of ammonia (including less than the 
one-thirty-millionth of efficient matter), when absorbed by a 
gland, should induce some change in it, which leads to a 
motor impulse being transmitted down the whole length of 
the tentacle, causing the basal part to bend, often through an 
angle of above 180 degrees. 
Astonishing as is this result, there is no sound reason why 
we should reject it as incredible. Prof. Donders, of Utrecht, 
informs me that, from experiments formerly made by him and 
Dr. De Ruyter, he inferred that less than the one-millionth 
ofa grain of sulphate of atropine, in an extremely diluted 
* Miller’s ‘Elements of Chemistry,’ part ii. p. 107, 3rd edit. 1864. 
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