Chapter XIV 

 THE UTRICULARIA TRAP 



General description of the trap ; terminology. — Historical account. — Anatomy and physi- 

 ology of the trap. — Two mechanical types of trap as regards the posture of the door (the 

 vulgaris-biovularia-purpurea type. The capensis-caerulea-cornuta type. The monanthos- 

 dichotoma-Polj'pompholyx type). — The variety of traps. — Digestion; the fate of prey. 



In the account of the character of the various sorts of Utricu- 

 laria already given, their arrangement in groups or types was based 

 on the character of the traps. In order to explain the workings of 

 all of them we shall begin by a detailed examination of the longest 

 studied and best known, that of Utricularia vulgaris and its close 

 relatives. What we learn of this we may then use as a basis for com- 

 parison with other types. 



The traps have been called urceoli, ampullae, vesiculae, utriculae, 

 pitchers, bladders, or traps. The most widely accepted term, blad- 

 der or vesicle, or the Latin, vesiaila, is not so bad as it seems, since 

 a bladder has an opening guarded by a valve in the form of a sphinc- 

 ter muscle which keeps it closed except under certain physiologi- 

 cal conditions when the muscle is temporarily relaxed. It was called 

 a pitcher by analogy with other carnivorous plants (Staff), but 

 this suggests a passive trap, and it is anything but that. Utricle 

 (utriculus), a small bottle with yielding sides (of skin or leather), 

 presumes a stopper. "Trap", used in this work, precisely fits, be- 

 cause the mechanism is that of an elaborate trap which is set automat- 

 ically and, after capturing prey, resets itself repeatedly, by observation 

 as many as fourteen times, and this is certainly not the limit. 



A description, in general terms, of the trap. Terminology. — The 

 vulgaris type of trap is a small flattened pear-shaped hollow body 

 attached to the plant by means of a stalk placed laterally, and trun- 

 cated obliquely across the narrow end, where occurs the mouth of 

 entrance. The stalk side is ventral; the opposite dorsal. The edge 

 of the mouth carries in most cases a pair of branched antennae, and 

 the sides some slender elongated bristles (27 — 7). These form a sort 

 of funnel leading to the entrance, acting as guides for prey. In some 

 species these appendages are absent or much reduced in size {U. oli- 

 gosperma). Because of the flattened shape we may speak of the sides 

 and the edge of the trap. The sides may be convex or concave, 

 as first clearly recorded by Erocher, according to physiological cir- 

 cumstances. When the trap is set, they are concave; after action, they 

 are less so, and the trap has now a more rounded form. Scattered 

 over the outer surface there are numerous small spherical glands, de- 

 void of cuticle, which give off mucilage. These glands are common to 

 the whole plant surface. 



The entrance {26 — i, 2) is guarded by two valves, a larger, 

 the door, and a smaller membranous one, the velum (Lloyd 1929). 

 The door is attached to the trap along a semicircular hne on the 



