Chapter XII — 207 — Dionaea and Aldrovanda 



the approach of the plasmolyte, as Czaja also found for Utricularia. 

 At the most, the cells display a systrophic contraction, but there is 

 no quantitative relation to the concentration of the plasmolyte 

 (Ashida). By watching the creeping in of the plasmolyte through 

 the cut ends of cells, Czaja estimated the osmotic equivalent to be 

 about m/3 KNO3. 



A plasmolyte has the effect of immobilizing the trap by the with- 

 drawal of water. For sugar (sucrose) immobilization occurs in from 

 40 seconds to 7.5 minutes for solutions of the concentrations 0.50 M. 

 to 0.1 1 M. according to the age of the leaf, the younger being more 

 easily affected. They react on stimulation till immobilization sets 

 in. On immersion in the solution (0.2 M. sucrose), the trap opens 

 a little beyond the normal, due perhaps to the withdrawal of water 

 weakening the bending force of the outer epidermis and the middle 

 layer. The springiness of the walls is, however, retained to some 

 extent, and they will spring open if closed by force, unless too far. 

 When left for some hours (six) in a 0.15 M. glycerine solution the 

 power of movement is recovered, due perhaps to the penetration 

 of the solute into the cells. Rapid changes of concentration in either 

 direction can stimulate, causing partial closure, but it is evident 

 that the immobilising effect and that of stimulation are antagonis- 

 tic. Only traps which are not completely immobilized can react at 



all. 



Neutral salts. — Czaja found only a "narcotizing effect." Ashdda, 

 however, found also that salts in solution can stimulate, for, though 

 strong solutions may quickly immobilize, their first effect is stim- 

 ulation and the traps close. Even in a saturated solution of KCl 

 the traps reacted within 1.6 to 2.6 seconds according to the age of 

 the trap, the younger the quicker. Similar behavior was found for 

 some other salts. 



Acids and alkalis. — When Ashida exposed traps to low concen- 

 trations of acetic acid and of HCl (0.005 to 0.05 N.) they closed after 

 various rather irregular periods from 29 to 2 minutes, respectively. 

 Since osmotic pressure is regarded as not entering in, Ashida tried 

 combining an acid with a non-electrolyte (acetic acid with sucrose) 

 and found that the reaction time was reduced, and that the more 

 sucrose is present, the shorter the reaction time. Two possible ex- 

 planations present themselves. Sucrose, even much below the concen- 

 tration which can stimulate osmotically, may help the stimulating 

 effect of the acid, an additive effect; or the permeability of the proto- 

 plast to acid may be increased during partial plasmolysis. Ashida 

 favors the latter alternative, for the additive effect is not observed 

 in young traps, in which osmotic and chemical stimulation alone 

 procure quicker responses. The second alternative also receives support 

 from the observations of Scarth (1927) that acid dyes penetrate 

 Spirogyra cells more readily when the protoplast is changing its vol- 

 ume during plasmolysis. 



Where now is the stimulus perceived? From applying acid to the 

 different leaf surfaces, Ashida found that when it was put on the 

 upper surface the response was obtained more quickly, indicating 

 that the joint cells of the sensitive hairs are the points of perception, 



