144 PLANTS WHICH EXHIBIT MOVEMENTS IN THE CAPTURE OF PREY. 



species of Drosera, is the presence of the delicate wine-red filaments, clavate 

 at their free ends and each supporting a glistening droplet of fluid, which stand 

 out from the leaves, and whose function is essentially the same as that of the 

 glands, stalked and sessile, on the leaf of Pinguicula. These filaments only 

 proceed from the upper surface and margin of the sun-dew leaf. The under surface 

 is smooth and hairless, and in many species, including the Drosera rotundAfolia 

 depicted on the plate, it rests upon the damp mossy ground. In this particular, 

 and also in the circumstance that all the leaves of each individual are adpressed to 

 the ground and grouped in a rosette or radially around the central slender flower- 

 ing-stem, there exists a very obvious analogy between Drosera, and not Pinguicula 

 alone, but many other carnivorous plants, such as Sarracenia, Heliamphora, Cepha- 

 lotus, and Dioncea, the fly-trap presently to be described. 



The filaments or tentacles projecting from the upper surface and margin of the 

 leaf look like pins inserted in a flat cushion and are of unequal size. Those which 

 stand up perpendicularly from the middle are the shortest, and those which radiate 

 from the outermost edge are the longest (see fig. 26 i ). Between these extremes 

 are intermediate lengths gradually leading from the one to the other. There are 

 on a leaf, in round numbers, about two hundred of these tentacles. The clavate 

 head at the free extremity of each must be regarded as a gland. It secretes 

 a clear, thick, sticky matter which is readily drawn out into threads, and which 

 shines and glitters in the sunlight like a drop of dew, whence the plant has derived 

 its name of sun-dew. Shocks occasioned by wind or the dropping of rain do not 

 excite any kind of movement in the tentacles. If grains of sand are blown upon 

 them by the wind, or if little bits of glass, coal, gum, or sugar, or minute quantities 

 of paste, wine, tea, or any other non-nitrogenous substance are brought by artificial 

 means into contact with the enlarged extremities of the tentacles, the exudation of 

 liquid at the places in question is augmented, and the secretion also becomes acid, 

 but there is no elimination of pepsin, and no change of importance ensues in the 

 direction of the tentacles, or the attitude of the leaf-margin. But the moment 

 a small insect, mistaking the glittering drops on the tentacles for honey as it 

 flies by, alights on the leaf and so touches the glands, or upon the artificial 

 placing of particles of nitrogenous organic matter, such as flesh or albumen, on the 

 tentacle-heads, there ensues, as in the case of Pinguicula, an increase in the dis- 

 charge of acid juice, as well as the addition of a ferment to its composition. The 

 action of this ferment on albuminous compounds is entirely similar to that of 

 pepsin, and we may even go so far as to speak of it as pepsin. 



The insects that fly on to the leaves and are caught by the sticky juice try to 

 disencumber themselves by stroking the viscous matter off with their legs, but they 

 only besmear themselves still more, and are soon plastered all over the body, and 

 have their movements greatly impeded by the secretion. Their efforts to save 

 themselves soon cease, the orifices of their respiratory organs are covered with the 

 juice and choked, and after a brief interval they die from suffocation. All these 

 phenomena correspond, in the main, to those occasioned by identical causes in the 



