THE PERMEABILITY OF CELLS 537 



Judging from Hormann's ('98) researches and the comparison 

 he has drawn between the rotating plant protoplast and muscular 

 contraction a difference in permeability was to be looked for. 

 The cessation of streaming induced by thermal, mechanical, 

 chemical and electrical means strongly suggests that a shock- 

 stoppage is comparable to muscle contraction and depends on a 

 similar conditioning change. Even the details connected with elec- 

 trical stimulation run parallel. According to Hermann the pass- 

 ing of a constant current through a rotating Nitella cell causes a 

 cessation of movement at the cathode on the make and at the 

 anode on the break. While the current is passing the streaming 

 is slower at the cathode. A wave of shock stoppage may be pro- 

 pagated from one region of a leaf to another and when tested 

 electrically the stopped regions are found to be negative to rotat- 

 ing ones just as the region of a muscle in contraction is negative 

 to an uncontracted area. 



We might therefore consider that protoplasmic streaming is 

 in some way connected with a high degree of electrical polariza- 

 tion, a low surface tension and a surface membrane relatively 

 impermeable to soluble substances, states typical of the resting 

 condition of many types of cells. Each of these three conditions 

 undergoes a change in the opposite direction, on 'stimulation' 

 of the cell. 



As stated before I have been unable to detect any constant 

 differences in permeabiUty (or resistance) of rotating and non- 

 rotating cells to KOH or NaOH. It is quite possible that several 

 factors each of which alone may be sufficient to prevent rotation, 

 are involved. 



d. The concentration of alkali which stops rotation: — InNH40H 

 {to to 8^0) rotation ceases just at the point where the bright pink 

 sap begins to turn dull pink before finally becoming yellow. In 

 NaOH the rotation ceases, begins again and finally ceases per- 

 manently loQg before the initial dull pink of the color change 

 appears. The description of the two experiments in which the 

 changes in individual cells was observed is as follows: 



