124 



PLANTS WITH TRAPS AND PITFALLS TO ENSNARE ANIMALS. 



In each pitfall there are always three kinds of contrivance to be distinguished: 

 first, a device for the allurement of animals; secondly, an arrangement for entrap- 

 ping the prey enticed, which at the same time prevents individuals once imprisoned 

 from returning and escaping through the entrance hole; and thirdly, a structure 

 for causing the decay or dissolution of the dead animals at the bottom of the pit- 

 falls, and for rendering possible the absorption of the products of decomposition 

 as nutriment. The means of allurement are similar to those which cause the visits 

 ■of small creatures to flowers, that is to say, principally honey and bright and 

 varied coloration, whereby the nectar -secreting spots are recognized from afar, 

 especially by flying insects. The escape of animals when they have once entered 

 the cavity of a petiole is prevented, as has been already mentioned, by a fringe 

 of sharp hairs pointed downwards, or by various spinous structures on the inner 





Fig. 19.— Spinous Structures in tlie Pitfalls of Carnivorous Plants. 



1 Genlisea; a piece of the tube seen from inside. 2 Heliarnphora nutans; spines on tlie walls of pitfalls, s Snrracenia 

 purpurea; a piece of the lining of the pitcher near tlie orifice seen from insitle. * Sarracenia purpurea; longitudinal 

 section through the membrane covered with spinous bristles in the lower part of the pitcher. ^ Nepenlhcs hybrida; 

 fringe of spines at the orifice of the pitcher, i, 2, 4^ s greatly magnified ; s sliglitly magnified. 



surface of the cavity. The decomposition and dissolution of the prey are effected 

 by fluids secreted by special cells at the bottom of the utricles and pitchers. 



But although in respect of the consecutive and co-ordinate operation of these 

 three kinds of contrivance, all ascidia- bearing and pitcher -plants resemble one 

 another, there are considerable individual divergences as to structure and function 

 that it is well worth while to study in some detail the most noticeable of them. 



One of the most noteworthy is the genus Genlisea, which is nearly related to 

 Utriculariace« in the structure of its flowers and fruit. It is composed of a dozen 

 species growing in water and marshy places. Of these one is a native of tropical 

 and southern Africa, whilst others are found in Brazil and the West Indies. In 

 addition to ordinary leaves, which in them are spatulate, most of the Genliseae 

 possess leaf-structures metamorphosed so as to constitute pitfalls. Each pitfall 

 consists of a long, narrow, cylindrical utricle, which at its blind end is enlarged 

 into a bladder, whilst at the narrow orifice at the opposite end are placed two 

 peculiar ribbon-shaped processes twisted spirally. The orifice of the utricle is set with 

 very small sharp teeth bent inwards; and the tubular part of the utricle has its 

 inner surface lined throughout with innumerable little bristles, which arise from rows 



