IRREGULAR NUTRITION 



241 



foothold on the converging walls, there is no escape. Death and 

 digestion follow. 



The secretion within the pitcher is exuded by numerous large, button- 

 shaped glands upon its inner surface. Each is covered on its upper 

 side by a downward drooping hood, which effectually prevents its use 

 as a step in climbing up out of the fluid. The presence of an insect 

 in the base of the pitcher stimulates the glands to secrete digestive 

 enzymes which convert the proteins of the insect body into soluble 

 compounds suitable for absorption by the cells of the pitcher. Some- 



Fig. 167 a. 



Bladder of Utricularia vulgaris in front view. The semi-circular 

 entrance is seen, closed by the lid, which is attached to the rim 

 along the top and part-way down the sides. Four bristles project 

 from the base of the lid. Attached to the rim of the entrance are 

 the antennae and other hairs. ( x 33.) (From Skutch, New Phyt.) 



what similar pitchers are present in Sarracenia and Cephalotus, though 

 no secretion of enzymes has been demonstrated in them. 



The trapping arrangements in the Bladderwort (Utricularia), a 

 native aquatic insectivorous plant, are quite different (Fig. 167 a). The 

 numerous minute bladders, replacing leaf-segments, are normally filled 

 with water, and are "set" as the result of an osmotic withdrawal 

 of water from the interior of the bladder by glands on the inner side 

 of the wall. The bladder-walls are in this way drawn in and brought 

 into a state of tension. If now an aquatic animal touches the bristles 

 which project from the lid of the bladder and so opens the lid, the 



B.B. 



