Chap. XL] GENERAL SUMMARY. 221 



whole length of the tentacle; this impulse exciting move- 

 ment often through an angle of above 180". I know not 

 whether to be most astonished at this fact, or that the pres- 

 sure of a minute bit of hair, supported by the dense secre- 

 tion, should quickly cause conspicuous movement. More- 

 over, this extreme sensitiveness, exceeding that of the most 

 delicate part of the human body, as well as the power of 

 transmitting 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 so- 

 dium all caused well-marked inflection, and none of them 

 were poisonous in small doses; whereas seven of the nine 

 corresponding salts of potassium produced no effect, two 

 causing slight inflection. Small doses, moreover, of some of 

 the latter salts were poisonous. The salts of sodium and 

 potassium, when injected into the veins of animals, likewise 

 differ widely in their action. The so-called earthy salts 

 produce hardly any effect on Drosera. On the other hand, 

 most of the metallic salts cause rapid and strong inflection, 

 and are highly poisonous ; but there are some odd exceptions 

 to this rule; thus chloride of lead and zinc, as well as two 

 salts of barium, did not cause inflection, and were not poi- 

 sonous. 



Most of the acids which were tried, though much diluted 

 (one part to 437 of water), and given in small doses, acted 

 powerfully on Drosera; nineteen, out of the twenty-four, 

 causing the tentacles to be more or less inflected. Most of 

 them, even the organic acids, are poisonous, often highly so; 

 and this is remarkable, as the juices of so many plants con- 

 tain acids. Benzoic acid, which is innocuous to animals, 

 seems to be as poisonous to Drosera as hydrocyanic. On the 

 other hand, hydrochloric acid is not poisonous either to 



