INFLUENCE OF MAGNETIC FORCES ON STREAMING 51 



conditions given. This retardation is best shown in Chara and Nitella, 

 which have large and sensitive cells, but is shown even in leaf-cells of 

 Vallisneria, Elodea, and in hair-cells of Tradescantia and Trianea * when 

 the pole-pieces are close together and the magnets fully charged. 



A more marked percentage retardation is shown when streaming is 

 rapid (viz. at 30 C.) than when it is slow (viz. at 10 C.). This is probably 

 because of the increased current, the latter being directly proportional to 

 the rapidity of flow across the field. If the action is not too prolonged, 

 the original tempo is usually resumed after a longer or shorter period of 

 recovery, but otherwise may be slower than before, and in some cases after 

 prolonged exposure (half to one hour) a progressive retardation ensues, the 

 cells ultimately dying. This is apparently not the result of any operative 

 injury, for outside the field similarly treated cells remain living for an 

 indefinite length of time. Sometimes a temporary or permanent localized 

 retardation is exhibited over certain areas of the cell, although streaming 

 is nearly normal in other parts. This points to a localized electrolytic 

 action. 



At each make and break of the field a current of very short duration 

 tends to pass around the cell, but it is so momentary that it never suffices 

 to produce a shock-stoppage. Very weak currents may sometimes at first 

 accelerate slow streaming, although stronger ones always retard. Hence 

 possibly arises the occasional slight acceleration seen on making the field. 

 The current produced at break is stronger than at make, and hence it 

 seemed possible that by summating the effects, a marked result might be 

 produced. Making and breaking the field 1,200 times in ten minutes pro- 

 duced no perceptible effect upon the movement of Infusoria and Bacteria, 

 although a slight retardation could usually be seen in Chara, Nitella, and 

 Vallisneria, especially when 2,000 makes and breaks were made in ten 

 minutes, or 3,000 in fifteen, and when the long axes crossed the lines of 

 force at right angles. This may possibly be because the current passing 

 round the short axis of the cell has a shorter path than round a long axis, 

 and hence encounters less resistance. 



Like Reinke, the author was unable to detect any movements or 

 changes of position of streaming threads in plant-cells, which could be 

 referred to the direct action of the magnetic forces. Since, however, a 

 feeble directive attractive force is actually exercised upon them when in 

 water, it is only a- question of obtaining a sufficiently powerful field to cause 

 them either to break or to set themselves along particular lines. It must 

 be remembered, however, that in thin threads, as the diameter decreases, 

 the surface-tension pressure increases, and hence also the relative rigidity 

 of the thread. 



- J The objects were placed on strips of glass four millimetres broad, and examined in water. 



E 2 



