470 On the Protoplasmic Streaming in Plants. 



Alcohols and anaesthetics when dilute may accelerate streaming, but 

 when more concentrated always retard it. Alkaloids, which are strong 

 nerve or muscle poisons, have relatively little action upon the streaming 

 protoplasm of plants. 



Weak electrical currents may accelerate streaming, strong ones 

 always retard it, while sudden shocks produce a temporary cessation. 

 The latent period of recovery decreases as the temperature rises up to 

 the optimum. Weak constant currents lower the optimal and maximal 

 temperatures for streaming. Cells are more sensitive to electrical 

 stimuli at moderately high temperatures than at very low or very high 

 ones, and the nucleus is fatally affected before the cytoplasm. 



The electrical conductivity of the protoplasm undergoes a slight 

 temporary increase on death, and it differs in the living cell from that 

 of the cell-sap and of the cell-wall. The effect produced by a weak 

 constant current bears no relation to its direction with regard to the 

 plane of streaming. 



There is little or no analogy between a shock-stoppage of streaming 

 and a muscular contraction, or between a nerve-muscle preparation and 

 a streaming cell. No permanently differentiated nervous mechanism 

 exists in plants, although temporary better-conducting channels may 

 appear as the result of prolonged stimulation or at certain stages in 

 the development of growing organs. Excitatory changes may be 

 transmitted in the protoplasm of a cell of Chara or Nitella at from 1 to 8 

 or 20 mm. per second (18 C.), but the rate of propagation from cell to 

 cell in tissues varies from Ol to 2 mm. per minute at 18 C. Neither 

 the chloroplastids nor any of the visible floating particles in the proto- 

 plasm have any power of independent movement, but are passively 

 carried with the moving stream. 



The only kind of energy which appears capable of producing 

 streaming movements under the conditions existing in plant-cells is 

 surface-tension energy, and this is probably brought into play by the 

 action of electrical currents which traverse the moving layers, and are 

 maintained by chemical action in the substance of the protoplasm. 

 These currents may act upon more or less regularly arranged bipolar 

 particles of emulsionised protoplasm in such a manner as to reduce 

 their surface-tension on the anterior side, or increase it on the posterior 

 one, hence producing streaming movement in a definite direction. 



