ELECTRIC EXPLORATION FOR GEO-PERCEPTIVE LAYER BY MEANS OF THE PROBE.

Experiment 185.—I shall now proceed to give a detailed account of the experiments. The first specimen employed was the shoot of Bryophyllum, one contact being made with the side of the stem, and the other with an indifferent point on the leaf which was always held vertical. In a particular experiment, the probe was introduced into the stem through 0·4 mm. and a feeble galvanometric negativity was induced as the wound-effect. After an interval of 5 minutes, this attained a steady value of -15 divisions. On the rotation of stem through +90°, the point A was above and a very much larger deflection of -82 divisions was obtained, being the result of summation of wound and geo-electric effects. On restoration of the plant to vertical position the geo-electric reaction disappeared, leaving the persistent wound reaction of -15 divisions unchanged. The true geo-electric reaction at a point 0·4 mm. inside the stem was thus -67 divisions which is the difference between -82 and -15 divisions. I obtained in this manner the excitatory reactions at different layers of the organ. The following table gives true values of geo-electric reaction at different layers of the stem as the probe entered it by steps of 0·4 mm.

TABLE XL.—SHOWING THE GEO-ELECTRIC REACTION AT DIFFERENT DEPTHS OF THE ORGAN (Bryophyllum).

Position of the probe.Geo-electric excitation
(galvanometric negativity).
Surface 5 divisions.
0·4 mm.-20 "
0·8 "-24 "
1·2 "-22 "
1·6 "-18 "
2·0 "-14 "
2·4 "-10 "
2·8 "- 5 "
3·2 " 0 "

The results given above, typical of many others, show that there is a definite layer in the tissue which undergoes maximum excitation under the stimulus of gravity, and that this excitation irradiates with diminishing intensity in radial directions inwards and outwards.

The geo-perceptive layer may thus be experimentally localised by measuring the depth of intrusion of the probe for maximum deflection of galvanometric negativity.

Localisation of geo-perceptive layer in Nymphæa: Experiment 186.—I employed the same method for the determination of the perceptive layer of a different organ namely, that of the flower stalk of Nymphæa. The electric reaction in Nymphæa, even under the prevailing unfavourable condition of the season, was moderately strong, being about three times greater than in Bryophyllum. A dozen observations made with different specimens gave very consistent results of which the following may be taken as typical. The probe was in this case, as in the last, moved by steps of 0·4 mm. at a time. Other examples will be given later where readings were taken for successive steps of 0·2 mm.

TABLE XLI.—SHOWING THE DISTRIBUTION OF INDUCED GEO-ELECTRIC EXCITATION IN DIFFERENT LAYERS (Nymphæa).

Position of probe.Galvanometer deflection.
Surface 0 divisions.
0·4 mm.-16 "
0·8 "-42 "
1·2 "-20 "
1·6 "-10 "
2·0 "- 2 "
2·4 " 0 "

It will be seen that as in Bryophyllum, so in Nymphæa, the geo-electric excitation increased at first with increasing depth of the tissue till at a depth of 0·8 mm. of the particular specimen the induced excitation attained a maximum value. The excitatory effect then declines till it vanished at a depth of 2·4 mm.