Chapter XII — 209 — Dionaea and Aldrovanda 



and we base our opinion with Darwin on the obvious analogy with 

 Dionaea. The closure of the trap into the narrowed posture reduces 

 the volume of fluid containing the digestive ferment, if present, thus 

 rendering it more effective (Darwin). Fermi and Buscaglione 

 (1899) offered some evidence that Aldrovanda is capable of digestion 

 by placing traps on sterilized gelatin, and finding that it was rendered 

 fluid. 



To the earliest observers the traps of Aldrovanda were thought 

 to be vesicles. The lifting of the plant from the water released the 

 traps so that air was inclosed, as in the case of Utricularia, but, as 

 CoHN pointed out, this air was purely accidental. That it enabled 

 the plant to float in the water, or at least assist in this when the 

 plant becomes loaded with prey (Fenner), in view of the fact that 

 it floats whether air is present in the trap or not, was seen to be a 

 gratuitous explanation. More recently Fenner advanced the idea 

 that gas is present as the result of chemical activity (digestion of 

 one kind or another). But this also has been questioned (Czaja 

 1924). That the presence of an air bubble assists in digestion 

 by reducing the water content of the digestion cavity, thus procuring 

 a more concentrated solution of ferments, that the water is absorbed 

 by the epidermis cells, and that the air bubbles assist in opening by 

 outward pressure (Fenner), are ideas which are superfluous in view 

 of the fact that adequate observation shows that the inclusion of 

 air is accidental. Fenner reports also that in vigorous leaves, after 

 the capture of prey, not only do the digestive glands, but also the 

 valve trichomes and the quadrifid hairs show signs of activity by 

 exhibiting changes in their contents. This requires further exami- 

 nation. It is true that Darwin had made similar observations indicat- 

 ing, it seemed to him, that the valve teeth and quadrifids do absorb, 

 but this evidence was regarded only as indicatory. 



When small prey are captured, the trap, stimulated by the vigorous 

 movements in the attempt of the prey to escape, remains closed for 

 some time according to the mass of the substance to be digested. 

 If the trap is overfed, as when supplied with large pieces of a flat- 

 worm (Czaja) it remains permanently closed, possibly because poi- 

 soned by the overplus of deleterious products, or perhaps because 

 growth had ceased. Reopening may be repeated several times under 

 favorable conditions of sufficiently meagre feeding. As already said 

 heavy feeding may, however, advantage the plant as much as several 

 smaller feedings. 



According to Schenk (on the authority of Cramer, 1877) Al- 

 drovanda was grown by him for two years in an inorganic salt solu- 

 tion without, apparently, any deleterious effect. Pfeffer cites this 

 in support of the non-obhgate character of carnivory in this plant. 

 This experience of Schenk's is surprising in the light of the expe- 

 riences of AsHiDA, who found it very difficult to grow the plant ex- 

 cept under rather special conditions. "No inorganic culture medium 

 could be found which would keep the plant in the normal form even 

 for a week". Aldrovanda grows in shallow water between the stems 

 of Typha, Zizania, Phragmiles, etc., which Hausleutner regarded as 

 merely protection against sun and wind. Asheda took a hint from 



