Page:Life Movements in Plants.djvu/151

Rh mm. by the true interval 1.6 seconds. Thus V = 15/1.6 = 9.4 mm. per second. We shall next consider the effect of current in modifying the normal velocity. The uppermost record (1) in Fig. 46 was taken under the action of an

46.—Record showing enhancement of velocity of transmission "up-hill" or against the current (uppermost curve) and retardation of velocity "down-hill" or with the current (lowest curve). N, normal record in the absence of current. ← indicates "up-hill" and → "down-hill" transmission.

'up-hill,' or 'against' current of the intensity of 1.4 micro-ampères. It will be seen that the time interval is reduced from 1.7 seconds to 1.4 seconds; making allowance for the latent period, the velocity of transmission under 'up-hill' current V$1$ = 15/1.3 = 11.5 mm. per second. In the lowest record (3) we note the effect of 'down-hill' current, the time-interval between stimulus and response being prolonged to 1.95 seconds and the velocity reduced to 8.1 mm. per second. The conclusion arrived at from this mechanical mode of investigation is thus identical with that derived from the electric method of conductivity balance referred to previously.