| Fig. 177. | Fig. 178. |
Fig. 177.—Curve of geo-electric excitation in different layers of Nymphæa. Ordinate represents geo-electric excitation; abscissa, distance from upper surface of flower stalk. The diagrammatic section underneath shows the position of geo-perceptive layer (starch-sheath) corresponding to maximum induced galvanometric negativity and positivity on the two sides.
Fig. 178.—The curve of geo-electric excitation in different layers of Bryophyllum.
A curve constructed from the data given above is seen in figure 177. The diameter of the flower stalk was 6·8 mm. The negative geo-electric reaction is seen to undergo an increase till it attains a climax at the depth of 1·4 mm. It then undergoes a continuous diminution till it becomes zero at the depth of 3 mm.; this neutral zone extends through 1 mm. When the probe enters a depth of 4·2 mm. measured from the upper side, it enters a region affected by the perceptive layer situated on the under side, the opposite physiological reaction being indicated by induced electric change of galvanometric positivity. This positivity reaches a climax at a depth of 5·4 mm. measured from the upper side, and 1·4 mm. when measured from the lower side. The points of maximum positivity and negativity are situated symmetrically on the opposite sides of the organ. The electric variation of maximum positivity on the lower side is comparatively feeble, less than half the corresponding maximum negativity on the upper side. Microscopic section showed that the geo-perceptive layers were the same as the starch-crescents.
Experiment 192.—I carried out similar experiments with the shoot of Bryophyllum. The results are given in Table XLV; the curve of the electric distribution along the diameter is seen in figure 178. The characteristics of this curve are the same as that of Nymphæa. The maximum galvanometric negativity occurred at the depth of 0·6 mm., and of positivity at a corresponding point on the opposite side.
TABLE XLV.—SHOWING INDUCED GEO-ELECTRIC DISTRIBUTION ACROSS THE STEM OF Bryophyllum (diameter = 3·6 mm.).
| Position of probe. | Galvanometric deflection. |
| Surface | 0 divisions. |
| 0·2 mm. | -24 " |
| 0·4 " | -45 " |
| 0·6 " | -63 " |
| 0·8 " | -21 " |
| 1·0 " | - 9 " |
| 1·2 " | - 6 " |
| 1·4 " | - 3 " |
| 1·6 " | 0 " |
| 1·8 " | 0 " |
| 2·0 " | 0 " |
| 2·2 " | 0 " |
| 2·4 " | + 3 " |
| 2·6 " | + 4 " |
| 2·8 " | + 9 " |
| 3·0 " | +36 " |
| 3·2 " | +21 " |
| 3·4 " | + 9 " |
| 3·6 " | 0 " |
Microscopic examination showed that the electric maxima in Bryophyllum coincided with the diametrically opposite points in the continuous endodermic ring. In Bryophyllum as in Nymphæa, the excitatory galvanometric negativity of the upper geo-perceptive layer is greater than the induced positivity of the lower layer in the ratio of about 2:1. But in a depressed condition of the tissue, the excitatory reaction is the first to disappear and the positive reaction persists, though with diminished intensity.
The geo-electric distribution in vigorous specimens seems to indicate that under the stimulus of gravity a marked excitatory reaction (contraction) takes place in the layer of cells contiguous to the upper geo-perceptive layer, and, a less marked positive reaction (expansion) occurs in layers contiguous to the lower perceptive layer.