272 DROSERA ROTUNDIFOLIA. Chap. XL 



for all physiologists admit that the salts of ammonia, 

 which must be brought in still smaller quantity by a 

 single shower of rain to the roots, are absorbed by 

 them. Nor is it surprising that Drosera should be 

 enabled to profit by the absorption of these salts, for 

 yeast and other low fungoid forms flourish in solutions 

 of ammonia, if the othpr necessary elements are pre- 

 sent. But it is an astonishing fact, on which I will 

 not here again enlarge, that so inconceivably minute a 

 quantity as the one-twenty-millionth of a grain of 

 phosphate of ammonia should induce some change in 

 a gland of Drosera, sufficient to cause a motor impulse 

 to be sent down the whole length of the tentacle ; this 

 impulse exciting movement often through an angle of 

 above 180°. I know not whether to be most astonished 

 at this fact, or that the pressure of a minute bit of 

 hair, supported by the dense secretion, should quickly 

 cause conspicuous movement. Moreover, this extreme 

 sensitiveness, exceeding that of the most delicate part 

 of the human body, as well as the power of transmit- 

 ting various impulses from one part of the leaf to 

 another, have been acquired without the intervention 

 of any nervous system. 



As few plants are at present known to possess glands 

 specially adapted for absorption, it seemed worth while 

 to try the effects on Drosera of various other salts, 

 besides those of ammonia, and of various acids. Their 

 action, as described in the eighth chapter, does not 

 correspond at all strictly with their chemical affinities, 

 as inferred from the classification commonly followed. 

 The nature of the base is far more influential than 

 that of the acid ; and this is known to hold good with 

 animals. For instance, nine salts of sodium all caused 

 well-marked inflection, and none of them were poison- 

 ous in small doses ; whereas seven of the nine corre- 



