140 DROSERA ROTUNDIFOLIA. fOiup. VII. 



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 am- 

 monia, therefore only a little more than twice as much as in 

 the weakest solution employed by me. The fact which ap- 

 pears truly wonderful is, that the one-twenty-millionth of a 

 grain of the phosphate of ammonia (including loss than the 

 one-thirty-millionth of efiicient 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. Bonders, of Utrecht, 

 informs me that, from experiments formerly made by him 

 and Dr. De Ruyter, he inferred that less than the one-mil- 

 lionth of a grain of sulphate of atropine, in an extremely 

 diluted state, if applied directly to the iris of a dog, paraly- 

 ses the muscles of this organ. But, in fact, every time that 

 we perceive an odour, we have evidence that infinitely smaller 

 particles act on our nerves. When a dog stands a quarter 

 of a mile to leeward of a deer dr other animal, and perceives 



Miller's * Elements of Chemistry,* part II. p. 107, 3rd edit. 1864. 



