390 Hooker: Movement in Drosera rotundifolia 



centration of osmotically active material dissolved in their cells 

 was measured by plasmolysis. For this purpose solutions of 

 potassium nitrate and glucose were prepared. The osmotic con- 

 centration of plant cells may be compared with the concentrations 

 of these substances in terms of their relative osmotic values. 

 Consequently osmotic concentrations will be measured in atmos- 

 pheres as follows: 



Solutions of KNOs Solutions of glucose 



Atmospheres in percentages in percentages 



S 1-43 3-85 



6 I-7I 4-62 



7 2.00 5-40 



8 2.29 6.17 



9 2.57 6.95 



10 2.86 7-71 



II 3-14 8.48 



12 3-43 9-25 



13 3-71 10-02 



14 4.00 10.80 



IS 4-29 11-58 



Tentacles of the Drosera were removed from the leaf with 

 forceps, placed in prepared solutions, mounted and examined under 

 the high power of the microscope. Plasmolysis was found to be 

 most readily detected in slightly pigmented cells, and whenever 

 possible tentacles with stalks composed of such cells were selected. 

 In case aggregation occurred, the first traces of plasmolysis were 

 much more difficult to make out. Tentacles were treated and 

 examined when straight; just after bending in response to a tactile 

 stimulus; when fully bent; during unbending; and when again 

 straight. The first procedure was to place tentacles in each of the 

 prepared potassium nitrate solutions and to examine them for 

 traces of plasmolysis. The results obtained by this general 

 orientation were repeated and verified by numerous subsequent 

 experiments both with potassium nitrate and with glucose solu- 

 tions. The data given with glucose solutions were practically 

 identical throughout with the results furnished by the potassium 

 nitrate solutions. The final data given below are expressed in 

 terms of the most concentrated solution that failed to plasmolyze. 



The epidermal cells on the pedicels of the tentacles have 

 strongly cutinized outer walls which are impermeable to salt and 

 sugar solutions. The solution reaches the inner cells of the ten- 



