of the Protoplcumie Streaming in Plants. 469 



Of the different constituents of the cell, cellulose, albumin, and 

 chlorophyll are paramagnetic ; starch, sugar, oil, water, and probably 

 myosin also, are diamagnetic. Plant-cells usually, though not always, 

 place their long axes parallel to the lines of force in a magnetic field. 



The strongest magnetic field used exercised little or no direct effect 

 on streaming, although a pronounced secondary effect is produced on 

 prolonged exposure as the result of inductive action. 



The connection between certain forms of streaming movement, such 

 as occur in a few fungi, and metabolism is a wholly indirect one, but 

 this can hardly be a general rule. Indirect relationships exist between 

 streaming, growth, and assimilation, but no direct ones. Similarly 

 the nucleus exercises no direct but a pronounced indirect influence on 

 streaming. 



An organised arrangement of the emulsionised protoplasmic particles 

 is probably an essential condition for regular continuous streaming. A 

 great variety of agencies when suddenly applied seem to disturb this 

 arrangement momentarily, and hence produce a temporary cessation of 

 streaming. This shock-effect results from sudden changes of concen- 

 tration, sudden falls or rises of temperature, momentary electrical 

 excitation, and the sudden application of various poisons. 



The minimal, optimal, and maximal temperatures for streaming vary 

 according to the plant or cell examined, and also depend upon (1) the 

 age or condition, (2) the external medium, (3) the duration of the 

 exposure, (4) the supply of oxygen, (5) the rapidity with which the 

 temperature is raised or lowered. 



At temperatures above 3(T C. the velocity immediately assumed is, in 

 the absence of a shock-effect, always greater than that shown a few 

 hours or a few minutes afterwards. Between 10 ' and 30 C. the 

 permanent velocity is almost immediately assumed. Below 10 C. the 

 acceleration due to a rise of temperature frequently does not become 

 fully manifest until after a certain lapse of time. 



In the case of facultative anaerobes, the response to changes of tem- 

 perature is less pronounced in the absence of oxygen than in its 

 presence. With short exposures the optimum and maximum points 

 are raised, but with prolonged ones the maximum temperature is 

 lowered by the absence of oxygen. 



Strong light retards streaming, while weak light may indirectly 

 accelerate it in chlorophyllous cells. It is still doubtful whether 

 streaming is affected by directly impinging electro-magnetic wave- 

 vibrations other than those of light. 



Mechanical disturbances may act as inhibitory stimuli, and may be 

 propagated internally in the form of pressure-waves. 



Food-materials exercise both a direct and an indirect effect upon 

 streaming. Acids, alkalies, and metallic poisons all retard streaming, 

 and may cause a temporary shock-stoppage when suddenly applied. 



2 L 2 



