Chapter XII — 205 — Dionaea and Aldrovanda 



individual cell must be less, since the total difference as between the 

 inner and outer epidermis is distributed throughout the tissue of, it 

 may be, some dozen cells in thickness. It is quite possible, therefore, 

 to extend the explanation given above for Aldrovanda to Dionaea, at 

 the same time excluding the loss of turgidity from the parenchyma, and 

 refer the whole movement to the action of the epidermis alone. This, 

 of course, does not square with Brown's explanation, but it neverthe- 

 less deserves consideration. 



Reference has already been made to the fact of sensitivity, its 

 seat and the varying response of leaves of various ages. We inquire 

 now more particularly into the responses to various types of agents, 

 whether stimulatory or otherwise. Under conditions of nature, within 

 the ordinary limits of temperature during the growing season, it has 

 been found that stimulation through pushing against the sensitive 

 hairs by animals, such as water fleas, spiders, etc. of small size, pro- 

 cures closure (shutting and narrowing). The trap then usually has 

 caught a small total amount of food material which is digested. In 

 the course of a few days (5-6, Czaja 1924) the traps reopen and are 

 ready to act again. This may be repeated by the same trap several 

 times, the number depending on the size of the prey caught and 

 the amount of undigested remains. The possible activity in repeated 

 response and reopening is certainly not so limited as thought by 

 Fenner. 



If, however, the prey is large and fills the digestion cavity (Czaja 

 used for experiment pieces of flatworm), the trap may never open 

 again. This may be due to the time involved, so that the trap passes 

 through its growth period and loses its sensitivity, or the production 

 and accumulation of substances having a poisonous effect. Too much 

 feeding is known to have a deleterious effect in other carnivorous 

 plants. This argues little or nothing in regard to the total value of 

 the process, since one long feeding may be of as much use to the 

 plant as several short ones. 



The observation of Burdon-Sanderson on Dionaea, that response 

 can be obtained by electrical stimulation, was the beginning of a num- 

 ber of studies of interest in the field of general plant and animal 

 physiology, leading to the examination of various agents on the ac- 

 tivity of the trap. By means of the electric current it has been pos- 

 sible to analyze the response into time phases. Czaja determined 

 the intensity of threshold stimuli to be 0.91 • lo"*^ Coulomb for an 

 opening shock, and 0.24-10"^ for a closing shock. By repeated ap- 

 plication of smaller shocks he found that there is a summation of 

 stimuli. AsHroA used this method for further analysis of the response, 

 and found that for fully opened leaves the direction in which the 

 current engages the trap has its effect, which is greater when applied 

 transversely than longitudinally, from which it is inferred that the 

 stimulus is more effective when running parallel to the long cells of 

 the motile zone, than across, and that the latter is more sensitive to 

 this stimulus than are the sensitive hairs themselves. This may be 

 related to the various resistances offered by the tissues concerned and 

 the direction of the current through the individual cells. The possi- 

 bility of controlling the intensity of stimulation by means of the elec- 



