| Specimen. | Induced E. M. F. |
|---|---|
| 1 | 0·0005 volt. |
| 2 | 0·0011 " |
| 3 | 0·0010 " |
| 4 | 0·0015 " |
ELECTRIC RESPONSE IN THE GROWING REGION.
Experiment 183.—I next undertook an investigation on the electric variation induced in the growing region under the stimulus of gravity. The experimental difficulties are here greatly reduced, since the available area of contact for galvanometric connection is not so restricted as in the case of the root-tip. The specimen is securely mounted so that the root is vertical. It is next rotated in the vertical plane through +90°, so that the point A in the growing region occupied the upper position. The electric response in the growing region took place in a short time and was very distinct. The induced electric change at A was now galvanometric positivity indicative of increase of turgor and expansion.
The series of experiments were carried out in the following order. The specimen was first rotated through +90° so that A was above. The responsive electric variation rendered it galvanometrically positive. The root was rotated back to neutral position when the current disappeared. The root was next rotated through -90° and the responsive current became reversed, the upper B becoming electro-positive (Fig. 173). The alternative rotations through +90° and -90° were carried out six times in succession with consistent results. The interval allowed between one stimulation and the next was determined by the period of complete recovery. Growing fatigue was found to increase this period; at first it was seven minutes, at the second repetition it was ten minutes, and at the third time it was prolonged to fifteen minutes.
Fig. 173.—Diagrammatic representation of geo-electric response of growing region of root. (a) Rotation through -90° makes B, galvanometrically positive. (b) Vertical and neutral position. (c) Rotation through +90° places A above and renders it galvanometrically positive. (d) Additive effect on current of response, root-tip a negative, and growing region A positive.
I give below the series of electric responses induced by alternate rotations through +90° and -90°. The upper position was occupied by A in the odd series, and by B in the even series. In every case the upper side became galvanometrically positive.
TABLE XXXVIII.—GEO-ELECTRIC RESPONSE OF ROOT IN THE REGION OF GROWTH.
| Odd series. | Galvanometer deflection A, positive. | Even series. | Galvanometer deflection B, positive. |
|---|---|---|---|
| 1 | 20 divisions. | 2 | 18 divisions. |
| 3 | 16 " | 4 | 18 " |
| 5 | 10 " | 6 | 12 " |