Abnormal acceleration of growth under electric stimulus: Experiment 88.—For my present purpose I took a sub-tonic specimen of seedling of wheat, its rate of growth being as low as 0.05 µ per second. After electric stimulation the rate was found enhanced to 0.12 µ per second, or about two and-a-half times. I give (Fig. 82) two records obtained with two different specimens. In the first, the record was taken on a stationary plate (Fig. 82). The closeness of successive dots in N show the feeble rate of growth of the sub-tonic specimen, the wider spacing after stimulation, S, exhibit the induced enhancement of growth.
Fig. 82.—Enhancement of rate of growth in sub-tonic specimens of wheat seedling. First series of record on stationary, second series (b) on moving plate N, record before stimulation. S, after stimulation.
In the second experiment the records (Fig. 82b) were taken on a moving plate. The specimen was so extremely sub-tonic, that its normal record N appears almost horizontal. The greater erection of the curve, S, after stimulation demonstrates the induced acceleration of growth.
TABLE XX.—ACCELERATION OF GROWTH BY STIMULUS IN SUB-TONIC SPECIMENS.
| Specimen. | Stimulus. | Rate of growth. |
| Wheat seedling | Normal | 0.05 µ per sec. |
| After electric stimulation | 0.12 µ " " | |
| Kysoor | Normal | 0.30 µ per sec. |
| After 5' exposure to light | 0.40 µ " " | |
| " 30' " " | 0.27 µ " " |
In my previous Paper on the ‘Modifying Influence of Tonic Condition’ I showed that while the response of the primary pulvinus of Mimosa in normal condition is negative, i.e., by contraction, diminution of turgor, and fall of the leaf, the response of a sub-tonic specimen is positive, that is to say, by expansion, enhancement of turgor, and erection of the leaf. I have shown further that in a sub-tonic specimen the action of stimulus itself raises the tissue from below par to normal or even above par, with the conversion of abnormal positive to normal negative response.
I have in the present Paper shown that a parallel series of reactions is seen in the response of growing organs. In vigorously growing specimens the action of stimulus is negative, i.e., incipient contraction, diminution of turgor, and retardation of the rate of growth. But in sub-tonic specimens, with enfeebled rate of growth, the effect of stimulus is positive, i.e., by expansion, enhancement of turgor, and acceleration of the rate of growth. Continuous stimulation also raises the sub-tonic growing tissue to a condition at par, converting the response from abnormal positive to normal negative.