308 SUMMARY OF CURRENT RESEARCHES RELATING TO 



BOTANY. 



GENERAL, 



Including the Anatomy and Physiology of Seed Plants. 



Cytology, 

 including- Cell-Contents. 



Protoplasmic Streaming.* — Dr. Ewart's work on protoplasmic- 

 streaming embodies the results of a series of observations carried on 

 during eight years. 



The author concludes that the energy of movement is generated in 

 the moving layers themselves, which are retarded by friction against the 

 non-moving ectoplasm, and also, but to a much less extent, by friction 

 against the cell-sap. The velocity of streaming is largely dependent 

 upon the viscosity of the protoplasm, and therefore also upon the per- 

 centage of water in the latter, but osmotic pressure has little or no direct 

 influence upon the process. Gravity does not affect the streaming in 

 small cells and only to a very slight extent in the case of large cells ; 

 but may affect the velocity of floating particles of greater or less density 

 than the plasma. A calculation of the amount of work clone indicates 

 that the energy expended in streaming is only a very small fraction of 

 that produced by respiration. The force required increases enormously as 

 the diameter of the channel decreases, so that transference in mass of the 

 highly viscous ectoplasm through interprotoplasmic connections becomes 

 practically impossible. The relations between streaming, growth, and 

 assimilation are indirect ; and similarly the influence of the nucleus is an 

 indirect one. The minimal, optimal, and maximal temperatures for the 

 process vary with the plant or cell examined, and also depend upon (1)- 

 the age or condition of the subject of experiment, (2) the external 

 medium, (3) the duration of the exposure, (4) the supply of oxygen, 

 and (5) the rapidity with which the temperature is raised or lowered. 

 Strong light retards streaming, while weak light may indirectly accelerate 

 the process in chlorophyll-containing cells. Acids, alkalies, and metallic 

 poisons all retard the process and may cause a temporary shock-stoppage 

 when suddenly applied. Dilute alcohols and anaesthetics and weak 

 electrical currents may accelerate the process ; more concentrated solu- 

 tions and strong currents retard it. The chloroplasts have no active 

 power of movement, but are carried passively in the stream. 



As regards the source of energy, surface-tension seems the only kind 

 of energy capable of producing the streaming movements under the 

 existing conditions in plant-cells ; this is probably brought into play by 

 the action of electric currents traversing the moving layers, and main- 

 tained by chemical action in the substance of the protoplasm. These 

 electric currents may be supposed to act upon regularly arranged bipolar 



* Alfred J. Ewart. 'On the Physics and Physiology of Protoplasmic Streaming, 

 in Plants,' Oxford, PJ03, viii. and 131 pp. and 17 tigs. 



