ELECTRIC PULSATION IN DESMODIUM GYRANS. 413 
same phase; in such a case the points A and A’ would both 
be at a given moment in the same state—either of excitation 
or quiescence. But it has been shown that electric response 
can only take place when there is a relative difference in the 
excitability of the two contacts. In the present case, the electric 
variations at A and A’ being similar, one balances the other, 
and there is no resultant response. 
2. If the excitation of the two leafiets be not simultaneous, 
but if there be a constant phase-difference of half a period 
between the two—that is to say, if while A’ is in a state of 
quiescence A is most excited and vice verséd—then in the former 
case the responsive current in the plant will be from the 
excitable A to the quiescent A’; this will give rise to an upward 
Fig. 6. 
Electric interference-effects due to the excitations of the two opposite leaflets. 
electric pulsation. The excitation of A will then subside, while 
that of A’ will reach a maximum. The responsive current will 
therefore change its direction, and we shall get a negative or 
downward response. Under these conditions, the responsive 
pulses would be regular and alternately up and down. 
3. There is again a third case where the phase-difference 
is not exactly half a period. In practice this is often found 
to be the case. Again, the periodicity of each leaflet may 
not remain absolutely constant, and the phase-difference may 
therefore undergo a continuous change. Under these conditions, 
we may expect a somewhat complicated curve due to the 
algebraical summation of A and A’ effects. I give here (fig. 6) 
a record which T obtained under these conditions. 
