INFLUENCE OF GRAVITY UPON ROTATION 



Nitella (18-5 C.). 



Similar results were obtained with elongated cells of Vallisneria and 

 Elodea at 17 C., the figures given representing the velocities in mm. per min. 



Vallisneria. 



Elodea. 



In both the latter plants a curious anomaly may often be observed 

 if floating chloroplastids or oil globules are used to indicate the velocity 

 of the streaming plasma, for they sometimes appear to indicate more 

 rapid streaming upwards than downwards. Thus : down, 0-954 mm. per 

 min. ; up, 0-989 mm. per min. 



In nearly all cases it will be noticed that the difference between the 

 horizontal velocity and the upward velocity is greater than the difference 

 between it and the downward velocity, the mean velocity in a cell 

 placed with its long axis vertical being slightly less than when it is 

 horizontal. 



A difference of velocity is no longer perceptible in cells of Char a and 

 Nitella, in which the direction of rotation is in a plane cutting the long 

 axis of the cell at an angle greater than 15 to 20 degrees. 



It is possible that gravity exercises a very slight and barely per- 

 ceptible physiological retarding action in streaming when elongated cells 

 are placed vertically, and that by very powerful centrifugal forces a marked 

 retardation, or even a cessation of streaming, might be induced. The 

 apparent differences of velocity observed in the ascending and descending 

 streams have, however, mainly a purely physical origin. They are due to 

 the particles observed being different in density to the liquid in which they 



