288 LOCOMOTORY AND PROTOPLASMIC MOVEMENTS 



of Characeae in passing into the endoplasm become covered with a layer 

 of the motory protoplasm which he supposes to bound the endoplasm 

 externally, and so acquire a power of independent locomotion. All the 

 phenomena described may, however, be shown by dead bleached chloro- 

 plastids, and isolated chloroplastids never show any power of independent 

 locomotion or of orientation, however long they may remain living and 

 functionally active 1 . 



Frequently the starch-grains or chloroplastids may ball together and 

 form an obstruction round which the protoplasm flows until it is swept 

 away 2 . In this way and also by partial plasmolysis, variations in the 

 contour of the vacuolar membrane may be produced, while as the result 

 of exposure to high temperatures partial coagulation may influence the 

 direction and manner of streaming 3 , and by exposure to localized intense 

 light streaming may be restricted to the two unaffected ends of a cell 

 of Chara 4 . 



The Physics of Streaming Movement 5 . In spite of the fluid character of the 

 endoplasm, gravity exercises relatively little action upon the speed of ascent and 

 descent of particles of varying density 6 . Whatever the motor mechanism may 

 be, it is such that no backward reaction is exercised upon either the cell-wall or 

 cell-sap. The total resistance to flow depends upon the viscosity of the moving 

 liquids and upon the diameter and length of the cell. Any factor which decreases 

 the viscosity, such as a rise of temperature or an increase in the percentage of water, 

 will decrease the resistance to flow and hence will tend to increase the velocity of 

 flow. The relative resistance to flow is proportional to the square of the radius of the 

 moving portion of the cell, so that in very small cells the resistance to flow becomes 

 disproportionately great, and in the case of the minute interprotoplasmic connexions 

 between contiguous parenchyma cells flow in mass becomes practically impossible. 

 The amount of energy actually consumed in the production of the streaming cannot 

 be determined, but the theoretical consumption based upon the assumption that the 

 protoplast is a perfect machine is exceedingly small. Thus the energy used by 

 a streaming cell of Nitella represents only a theoretical consumption of 2 o CK) o o 

 of a gram of cane-sugar per annum per gram of plasma moving at a rate of 2 mm. 

 per minute in a cell of 0-4 mm. radius. In the smaller cells of ordinary plants less 

 than a tenth of a per cent, of the energy of respiration appears to be consumed in 

 the production of streaming movement. In the large cells of Chara and Nitella the 

 normal rate of streaming is more rapid than in the smaller cells of Vallisneria and 

 Elodea of lesser radius, but this is not necessarily the direct result of the relatively 

 greater resistance, for it is hardly likely that in all cases the same proportion is 



1 Ewart, Protoplasmic Streaming in Plants, 1903, pp. 107, 108. 



2 Meyen, Pflanzenphysiologie, 1838, Bd. II, p. 220; Nageli, I.e., p. 62; Hofmeister, Pflanzen- 

 zelle, 1867, p. 44; Rhumbler, Zeitschr. f. allgem. Physiol., 1902, Bd. I, p. 321. 



Ewait, I.e., p. 59. 



4 Pringsheim, Jahrb. f. wiss. Bot., 1882, Bd. XII, p. 326. 



5 For fuller details see Ewart, 1. c., p. 6 seq. e Cf. Ewart, 1. c , p. 23. 



