PLANTS UNDER MECHANICAL STIMULUS. 293 
Diphasic Vartation. 
When a plant is stimulated at any point, a wave of molecular 
disturbance is propagated outwards from the point of its 
initiation. This wave of molecular disturbance is attended 
by a wave of electrical disturbance. It takes some time for 
a disturbance to travel from one point to another, and its 
intensity may undergo a diminution as it recedes farther from 
its point of origin. This diminution is sometimes very rapid. 
Series of records under continuous stimulation. 
It will thus be seen that we might obtain responses even 
without injury or block in cases where disturbance is very much 
enfeebled on reaching a distant point. In such a case, on giving 
a tap near A, a responsive current would be produced in one 
direction, and a current in an opposite direction when the tap is 
given near B (fig. 178). Theoretically, then, we might find a neutral 
point between A and B, so that on originating the disturbance 
there the wave would reach A and B at the same instant, with 
the same intensity; the resulting electric disturbances at A and 
B will continuously balance each other and the galvanometer 
will show no current. On taking a eylindrical root of carrot, 
I have sometimes succeeded in finding a neutral point, which 
being disturbed did not give rise to any resultant current. But 
disturbing a point to the right or to the left gave rise to opposite 
: however, difficult to obtain an absolutely 
cylindrical specimen, as it always tapers in one direction. The 
conductivity towards an ascending direction 1s not exactly the 
same as that in the opposite direction. It is therefore difficult 
currents. It is, 
