INSECTIVOROUS PLANTS. 



399 



This is the bait which is cunningly provided, so that the 

 victim may be led pleasantly on its way to destruction. One 

 species of Nepenthes has no honey-glands on the inside of the 

 lid — viz., N. ampullar ia. Sir Joseph Hooker has shown why 

 this species is thus exceptional. Unlike all the other species, 

 its lid is thrown horizontally back, and therefore honey 

 secretion on a lid so placed would tend to lure insects away 

 from the pitcher instead of into it. Next comes the " conduc- 

 tive " surface, which occupies a variable portion of the upper 

 part of the interior of the pitcher. This surface is composed of 

 smooth, glassy cells, which afford no foothold to insects, and it is 

 generally studded over with minute reniform or crescentic ledges. 

 The remainder of the pitcher is occupied by the "secretive" 

 surface. This is thickly covered with glands resembling those 

 of the lid, but the depressions in which they are lodged have 

 their concavities directed downwards, resembling much in appear- 

 ance inverted waistcoat pockets. Hooker mentions that in N. 

 Bafflesiana three thousand of these glands occur in a square inch. 

 An acid fluid, which is secreted by these glands, is formed at the 

 bottom of the pitcher, and is present in considerable quantity 

 before the lid of the pitcher opens. This fluid has the same 

 digestive properties as that of Drosera, Dionasa, and Pinguicula. 

 Animal matter put into the pitchers, such as small pieces of meat 

 or white of egg, becomes acted on in a very short time. It would 

 appear, however, that the digestive power of the secretion is not 

 due entirely to the fluid first secreted by the pitcher, but that a 

 substance resembling pepsine in its action is given off from its 

 inner wall, chiefly after the placing of animal matter in the fluid. 

 In support of this idea Hooker states that very little action took 

 place on any of the substances placed in the fluid drawn from 

 pitchers and deposited in a glass tube, although the disintegra- 

 tion of the substances was three times more rapid in the fluid 

 than in distilled water. On the other hand, substances placed 

 in the fluid in the living pitchers were acted on in a very rapid 

 manner : cubes of boiled egg had their edges dissolved in twenty- 

 four hours, and their surfaces gelatinised. Fragments of fibrine 

 weighing several grains were dissolved, and totally disappeared 

 in two or three days ; while bits of cartilage weighing eight to 

 ten grains were greatly diminished and reduced to a transparent 

 jelly in three days. 



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