Ill Other Insectivorous Plants 47 



strongly, the nitrate even more so, and the phosphate most 

 of all. But the remarkable fact is the sensitiveness of the 

 tentacles to infinitesimal quantities. Thus the immersion 

 of a leaf in a solution of the last-mentioned salt, so weak 

 that each gland could absorb only about ooWooHTr °^ ^ 

 grain, is sufficient to produce complete inflection of the 

 tentacles. Though the particles of solid matter which 

 stimulate the olfactory nerv^es of animals, and so produce 

 the sensation of smell in animals, must be very much 

 smaller than this, as Mr. Darwin remarked, the fact 

 remains truly wonderful that the absorption of so minute 

 a quantity by a gland should induce some change in it, 

 which leads to the transmission of a motor impulse down 

 the entire length of the tentacle, causing the whole mass 

 to bend, often through an angle of more than 180°, and 

 this too in the absence of any specialised nervous system. 



It is not much to our present purpose to discuss the 

 numerous experiments which Darwin made on the action 

 of salts and acids, drugs and poisons on the leaves of the 

 sundew ; but the effects of organic fluids are important. 

 Darwin treated sixty-one leaves of Drosera with non- 

 nitrogenous solutions — gum-arabic, sugar, starch, dilute 

 alcohol, olive-oil, tea. The tentacles were not in a single 

 case inflected. He then applied to sixty-four other leaves 

 various nitrogenous fluids (milk, wine, albumen, infusion 

 of meat, mucus, saliva, isinglass), and sixty-three had the 

 tentacles and often the blades well inflected. Finally, 

 taking twenty-three of the leaves which had served for the 

 first experiment, and treating them with bits of meat or 

 drops of nitrogenous fluids, all save a few, — apparently 

 injured by exosmose caused by the density of the former 

 solution of gum, sugar, etc., — were distinctly inflected. 



Digestion. — That the sundew possesses power of digest 

 ing the insects which it catches is evidenced in great detail. 



