172 DROSERA ROTUNDIFOLIA. Cuar. VII. 
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, there- 
fore, 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 above 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 effi- 
cient 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 ° 
* Miller’s ‘Hlements of Chemistry,’ part ii. p. 107, 3rd edit. 1864, 
