But in the Woodsorrel these movements are not for protection against grazing animals.
There are other examples amongst plants of a distinct sudden movement which begins whenever part of the plant is touched. The movements of tendrils have been already referred to. The Venus' Fly Trap and the Sundew will be mentioned when we are discussing Insectivorous Plants. There are also several flowers in which the stamens suddenly spring up when they are touched by an insect (Barberry, Centaurea, and Sparmannia), and in Mimulus the style-flaps close when touched (see p. [70]).
All these cases seem to involve some sort of mechanism which replaces the nervous system of animals.
No very definite laws have yet been discovered as to the way in which plants are affected by electricity, but enough is known to show that there are many interesting discoveries in prospect.
Professor Lemström has made some interesting experiments in the Polar regions which go to show that the rich development of plant life in that desolate region may be connected with the peculiar electrical conditions of the Polar atmosphere; the aurora borealis, which is a common phenomenon there, being also produced by those conditions.
Several writers have claimed that slight electric shocks given at frequent intervals help the growth of plants and especially quicken the germination of seeds, but it can scarcely be said that this has been proved.
When a branch or leaf-stalk is wounded or injured by being tightly clamped in a vice, then it will be found that a current of electricity passes from the injured spot to the part that is untouched, and then in the reverse direction.
Changes of current are also produced when a leaf is suddenly exposed to light for a short time and then shaded.
One of the most interesting observations is that made by Major Squiers near Lorin Station, in America, where the California Gas and Electric Corporation of San Francisco has a long-distance transmission telegraph line. The power is transmitted at a voltage of 56,000 with a frequency of sixty cycles per second (three-phase). Major Squiers, from previous experiments, thought that a note corresponding to this frequency might be heard in a telephone receiver. The following was the result:—
"Upon connecting the telephone between two nails driven in any growing tree along the route of the line, and at a reasonable distance therefrom, the telephone responded to this note with great clearness, and when the distance was not more than 100 feet, the sound was very loud. For this experiment no microphone need be used, nor any source of electromotive force other than that induced in the tree itself, the telephone being connected directly between two nails driven into the tree....