Chapter XIV — 265 — The Utricularia Trap 



It seemed evident from all the foregoing that digestive ferments 

 are present, but principally in the traps. 



KiESEL (1924), however, took the opposite view. He found that 

 fragments of fibrin were digested in the traps, but if acidified with 

 0.2% HCl were not. The trap fluid, obtained by means of a fine 

 pipette directly from the traps and preserved under toluol showed 

 no power to digest fibrin, gelatin or albumin. He concluded that the 

 digestion in the traps of Utricularia is the work of microorganisms. 

 What these might be was investigated by Stutzer (1926). Traps 

 washed in sterile physiological solution were minced and the contents 

 thus obtained were sown on agar plates. He found bacteria of the 

 Bacterium coli group to be dominant and suggested that they play the 

 important role of digestion. Other bacteria play a secondary role. 

 Those of the kind found in the digestive tracts of insects etc., are also 

 to be met with, but these he thought play the same role in the traps 

 as there, namely, to conserve the nutrient mass during digestion and 

 hinder the development of putrefactive bacteria. It is possible, in ad- 

 dition, that Bacillus aquatilis communis, one of the soil bacteria, takes 

 some part in digestion, since it can digest albumin. 



And there the matter stands at the moment. On the one hand, 

 it is held that the presence of benzoic acid inhibits bacterial action, 

 and that any digestive action is the work of the ferments secreted by 

 the trap itself; on the other the digestion is referred to the activity of 

 bacteria. Hada (1930) takes a middle ground, holding that "the 



animals captured are decomposed not only by the enzyme secreted 



by the plant, but also by the bacteria which increase rapidly after the 

 death of the animals." Since his paper is in Japanese, I do not know 

 what evidence he puts forward. 



Prey and their fate. — The presence of sugar as well as mucilage 

 in the glandular hairs at the entrance of U. vulgaris, shown by Luetzel- 

 BURG, was thought by him to indicate that these hairs form a lure to 

 attract animals. The presence of special groups of glands near the 

 entrance in some species {e.g. U. cornuta) seems to support this view. 



While it is true enough that animal prey captured by the traps of 

 Utricularia sooner or later succumb and are digested, there are ex- 

 ceptions in organisms which are able to live and multiply in the re- 

 stricted space of the interior of the trap, notably Euglena, Heteronema, 

 Phacus (Hegner) and probably others, including diatoms and desmids, 

 often seen. There is at present no evidence of obligate relations; 

 these forms seem to be caught probably accidentally, and can live 

 inside the trap indefinitely, though Hegner states that when plants 

 are kept a long time in an aquarium, the Euglena runs out. Protozoa 

 when captured generally succumb, but some remain alive for a long 

 time, a fact noted long ago. The presence of decaying Paramaecia in 

 the trap does not affect the Euglenae. 



That Paramaecium is sometimes quickly killed and at others re- 

 mains alive for a long time (75 min. to 17 days) (Hegner) seems to 

 indicate that the physiological conditions in the traps are not always 

 uniform. Luetzglburg thought he detected a paralysing effect of 

 the extract which he used for digestion experiments on small crusta- 

 ceans, but that it must be weak. Hada advanced the idea that 



