172 DROSEEA ROTUNDIFOLIA. CHAP. 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-niillionth 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 ' Elenvmts of Chemistry,' part ii. p. 107, 3rd edit. 18G4, 



