INSECTIVOROUS PLANTS. 



397 



stand at rather less than a right angle to each other, and the 

 edges are set round with bristle-like projections, which inter- 

 lace like the teeth of a rat-trap when the leaf closes. The upper 

 surface of each lobe towards the midrib is thickly covered with 

 minute red glands, which give it a rosy appearance, and the lobes 

 also bear three erect sensitive filaments arranged in a triangular 

 manner. The filaments are further provided with a joint or 

 hinge near the base, so that when the leaf closes they fold down, 

 and thus escape injury. These filaments or hairs are sensitive 

 over their whole surface, and respond so readily to a momentary 

 touch that an insect alighting on the leaf is almost certain 

 to cause it to close. When touched a motor impulse is con- 

 veyed from the excited hair through the cellular tissue of the 

 leaf-blade to the midrib, the result being that the lobes instantly 

 close. This closing, however, is not at first perfect, the teeth only 

 slightly interlacing, so that if the insect is small it is allowed to 

 escape, but if it is large the glands are induced to secrete and 

 absorb the animal matter, which, according to Darwin, has the 

 effect of causing the lobes to press closely against the body of the 

 insect. The pressure is often so great that the outline of the 

 body of the insect can be seen on the outside of the leaf. When 

 the lobes are induced to close by mechanically touching the 

 sensitive hairs, they remain closed only for a short time ; but when 

 an insect is caught they remain closed for about eight days 

 generally. Darwin mentions a case where a leaf remained closed 

 for thirty-five days over a large Tipula. On an insect or other 

 animal substance being thus entrapped by a leaf, the peptic 

 glands on the upper surface of the lobes pour out an acid secre- 

 tion immediately the animal matter comes in contact with them. 

 Moist nitrogenous substances when placed on the glands of a 

 leaf, even although the sensitive hairs are untouched, not only 

 cause the glands to secrete, but the lobes slowly close. Eegard- 

 ing the capability of Dionaea to feed on nitrogenous matter, a 

 very simple experiment will be sufficient to convince the most 

 sceptical on this point. Let a small cube of white of egg be 

 enclosed in a leaf of the plant, and one can actually watch the 

 process of digestion going on day by day. By carefully inserting 

 the blade of a penknife between the lobes of the leaf and catch- 

 ing the marginal spines with the fingers, the lobes can then be 

 opened sufficiently wide to examine the interior. A good deal of 



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