iq2o] SCHLEY— GEO-PRESENTATION AND GEO-REACTION 77 



Osmotic pressure 



The osmotic pressure of the two flanks during the period of 

 presentation and response was determined by means of plas- 

 molysis. Weight molecular solutions of cane sugar and potassium 

 nitrate were used as plasmolyzing agents. The seedlings were 

 geotropically stimulated for varying periods of time. Portions 

 of the seedlings, including the region of response, were sectioned 

 (on the hand microtome) vertically, that is, from upper to lower 

 side of the horizontally placed shoot. The sections were placed in 

 weight molecular solutions of the plasmolyzing agent of such 

 percentages as previous experiment had shown to be close to the 

 plasmolyzing point. The series of weight molecular solutions was 

 graduated to intervals of one-half of 1 per cent. The accompanying 

 tables and graphs show the results of one each of the experiments 

 made. 



PLASMOLYSIS 

 (Using cane sugar as plasmolyzing agent) 



In normal shoots both sides plasmolyze at 42 per cent weight molecular 

 After 5 minutes' stimulation both sides plaSmolyze at 42 per cent 

 After 10 minutes' stimulation both sides plasmolyze at 43 per cent 

 After 45 minutes' stimulation upper side at 43, lower side at 44 per cent 

 After 1 . 5 hours' stimulation upper side at 43, lower side at 44. 5 per cent 

 After 5 hours' stimulation both sides at 43 per cent 



(Using potassium nitrate as plasmolyzing agent) 



In normal shoots both sides plasmolyze at 31 per cent weight molecular 



Stimulated 15 minutes both sides plasmolyze at 31 per cent 



Stimulated 30 minutes both sides plasmolyze at 32 per cent, upper general, 



lower a few cells 

 Stimulated 45 minutes upper faintly at 33, lower at 33/5 per cent 

 Stimulated 1 . 25 hours upper at 32, lower at 33 per cent 

 Stimulated 5 hours both sides at 32 per cent 



These results indicate that the osmotic pressure of the cell rises 

 as the time of stimulation increases, reaches a maximum at or 

 before visible response, and decreases as the response nears com- 

 pletion. The osmotic pressure is greater on the convex side during 

 the period of response. It is interesting to note that the maximum 

 acidity, as shown in a previous paper (18), is reached in 30 minutes, 

 while the maximum turgor is reached in 45 minutes. The results 

 of different investigators on the turgor change of stimulated shoots 



