138 DROSERA ROTUNDIFOLIA. [Chap. VII. 



nitrogenous organic fluids are powerless. As such minute 

 doses of the salts of ammonia affect the leaves, we may feel 

 almost sure that Drosera absorbs and profits by the amount, 

 though small, which is present in rain-water, in the same 

 manner as other plants absorb these same salts by their roots. 



The smallness of the doses of the nitrate, and more espe- 

 cially of the phosphate of ammonia, which cause the ten- 

 tacles of immersed leaves to be inflected, is perhaps the most 

 remarkable fact recorded in this volume. When we see that 

 much less than the millionth ' of a grain of the phosphate, 

 absorbed by a gland of one of the exterior tentacles, causes it 

 to bend, it may be thought that the effects of the solution on 

 the glands of the disc have been overlooked; namely, the 

 transmission of a motor impulse from them to the exterior 

 tentacles. No doubt the movements of the latter are thus 

 aided; but the aid thus rendered must be insignificant; for 

 we know that a drop containing as much as the yVrir of a 

 grain placed on the disc is only just able to cause the outer 

 tentacles of a highly sensitive leaf to bend. It is certainly 

 a most surprising fact that the tttVothjv of a grain, or in 

 round numbers the one-twenty-millionth of a grain (.0000033 

 mg.), of the phosphate should affect any plant or indeed any 

 animal ; and as this salt contains 35.33 per cent, of water of 

 crj'stallisation, the efficient elements are reduced to tvtj'httt 

 of a grain, or in round numbers to one-thirty-millionth of a 

 grain (.00000216 mg.). The solution, moreover, in these ex- 

 periments was diluted in the proportion of one part of the 

 salt to 2,187,500 of water, or one grain to 5000 oz. The 

 reader will perhaps best realise this degree of dilution by 

 remembering that 5000 oz. would more than fill a 31-gallon 

 cask; and that to this large body of water one grain of the 

 salt was added ; only half a drachm, or thirty minims, of the 

 solution being poured over the leaf. Yet this amount suf- 

 ficed to cause the inflection of almost every tentacle, and 

 often of the blade of the leaf. 



I am well aware that this statement will at first appear 

 incredible to almost every one. Drosera is far from rivalling 



* It Is Bcarcely noBslble to In lonjrth, and Btretch It along 



realise what a nillllon means. the wnll of a Inrse hall; then 



The best llliistrnllon which I mark off at one eml the tenth of 



have met with In that jrlven by an Inch. This tenth will reprc- 



Mr. Croll, who snys, Take a sent a hundred, and the entire 



narmw strip of paper 83 ft. 4 In. strip a million. 



