Chapter XII — 201 — Dionaea and Aldrovanda 



bent twice, followed by the closure of the trap. On the other hand 

 an old trap closed with one stimulus only, seen by Dr. E. Merl 

 and myself, as we were working jointly at the time. Another dis- 

 tinctly old trap responded to the eleventh stimulus, ten on one hair, 

 the eleventh on another. Many did not respond at all. Ashida 

 made quite similar observations. De Lassus (i86i) had already 

 observed that young traps are somewhat more sensitive than older 

 ones. It became apparent that this lack of uniformity, while a fact, 

 does not mean lack of dependability of the trap in nature, since 

 the prey which ventures into an open trap must needs stimulate 

 many hairs many times if it moves about. If the trap closes par- 

 tially (see below) so that the prey cannot escape, the continued move- 

 ments insure a further stimulation, and complete closure is assured. 



The mode and mechanics of closure may now claim our attention. 

 We have seen that each lobe displays two concentric regions, an inner 

 thicker, and an outer very thin and pliable, and edged with a valve. 

 If a relatively weak stimulus is applied, the lobes close till their 

 free edges meet. Unless additional stimulus is added, in the course 

 of a short time (20 to 30 min.) the lobes begin to open, and shortly 

 resume their original postures, at some 45 or 50 degrees from each 

 other. If, however, a sufificiently strong stimulus, or repeated stimuli 

 be used, the lobes continue to close still further. This is possible 

 because the free-side lobe flexes under pressure against the bristle- 

 side lobe, at first just inside the valvular edge, the flexure extending 

 until most of the two regions are mutually appressed {ig — 21). 

 The two marginal valves become bent under this mutual pressure, 

 the teeth intercrossing so as to prevent prey from escaping when 

 the lobes are first closed. Resulting from the whole movement, the 

 thick regions have moved together and a space has been inclosed by 

 the meeting of their outer Hmits, forming a smaller but more ines- 

 capable prison {ig — 22). Here the digestive glands begin their 

 work of digestion, and in the course of time the prey is disintegrated 

 and the products absorbed. If a plant is Hfted out of the water, 

 the water films stimulate the traps to closure, and in closing, air 

 is entrapped. The idea that the traps were hollow, closed organs, 

 held by Monti, led him to use the descriptive name ''vesiculosa.''' 

 CoHN (1850) and de Lassus (1861) found this to be a mistake. 



The mechanism of movement. — The sensitivity of the trap was 

 first observed by Auge de Lassus, who was cognizant of the facts 

 regarding Dionaea and Drosera in 1861. The fact was rediscovered 

 by B. Stein in 1873 (mentioned by Cohn in 1875) who found that 

 it is the slender hairs which are capable of receiving stimulus, and 

 recognized the analogy in this detail with Dionaea. Additional con- 

 firmation was offered by Mori (1876). Goebel showed more com- 

 pletely this analogy by demonstrating the hinge of the sensitive 

 hair. Czaja (1924) studied the effect of various kinds of stimula- 

 tion. He incorrectly regarded the midvein as a hinge about which 

 the valves rotate to approach each other in closure. 



It has remained for Joji Ashida to make a studious attempt to 

 elucidate the mechanism of response, following that of Brown and 

 Sharp for Dionaea. Ashida first made clear where the exact re- 



