Page:Researches on Irritability of Plants.djvu/50

Rh means of which the rays can be focused upon any point that is desired.

I have found that Mimosa and other sensitive plants show certain very remarkable excitatory effects under the action of a constant current. The characteristic feature of these is that excitation is not induced during the passage Of the current but only at its initiation or cessation. The excitatory effect in this case is further conditioned by the point

of entry, or anode, and that of exit, or kathode. The specific characteristics of this mode of stimulation will be found fully described in the chapter on the Polar Effects of Currents in Excitation. It need only be mentioned here that, in the matter of all these peculiar effects, the plant tissue behaves in a manner exactly similar to the animal tissue. A series of records obtained from Mimosa by the stimulus of a constant current are shown in fig. 8.

Another practical method of stimulation is that of condenser discharge. The condenser consists essentially of two conducting-plates—which may be two sheets of