32 Chapters in Modern Botany CHAP. 



a modified leaflet is a simple but effective trap. It is a 

 hollow chamber, about J- s of an inch in length, entered 

 by a thin transparent door or valve which opens inwards 

 only and allows of no egress, for it shuts instantly, as if 

 with a spring, against an anterior thickened collar or pro- 

 jection around the mouth. 



These traps are very fatal to small Crustaceans, popu- 

 larly known as water-fleas, which swarm in every fresh- 

 water basin. Pursued by their enemies, or attracted 

 perhaps by a slight mucilage which is exuded from glands 

 on the door of the trap, or prompted it may be by wayward 

 curiosity, the water-fleas clamber on six or seven long stiff 

 bristle-like processes which project from the mouth of the 

 bladder. So far they are safe enough, but if they explore 

 farther, and push before them the inward-yielding door of 

 the bladder, they are within a prison from which there is 

 no escape. For a day or two they may live, but the trap 

 becomes crowded with prisoners, and they die. No diges- 

 tion occurs, but the bodies of the animals are decomposed 

 by Bacteria, and the products of decomposition are ab- 

 sorbed. That these products are useful to the bladderwort 

 is confirmed by Biisgen's observation that those plants 

 from which all water-fleas were artificially excluded did not 

 flourish so well as those in normal conditions. Darwin 

 believed that the four-fold hairs which occur abundantly 

 over the internal surface of the bladder were absorbent 

 structures, but this is by no means certain. Indeed these 

 peculiar hairs are connected by intermediate forms with 

 the slime-secreting hairs found outside the bladders, for 

 instance on the door. It is worth noting that such hairs 

 are to be found in many aquatic plants quite innocent of 

 insect catching; as, for instance, on the leaves of Calli- 

 triche verna. Chodat, and after him others, have shown 

 that they arise from cells which under ordinary circum- 



