Another very curious effect that I have noticed is that when a plant approaches its death-point by reason of excessively high or low temperature, not only is its general responsiveness diminished almost to zero, but even the slight response occasionally becomes reversed.
Fig. 36.—After-effect of Cold on Ivy, Holly, and Eucharis Lily
a. The normal response; b. Response after subjection to freezing temperature for twenty-four hours.
Influence of high temperature, and determination of death-point.—I next tried to find out whether a rise of temperature produced a depression of response, and whether the response disappeared at a maximum temperature—the temperature of death-point. For this purpose I took a batch of six radishes and obtained from them responses at gradually increasing temperatures. These specimens were obtained late in the season, and their electric responsiveness was much lower than those obtained earlier. The plant, previously kept for five minutes in water at a definite temperature (say 17° C.), was mounted in the vibration apparatus and responses observed. The plant was then dismounted, and replaced in the water-bath at a higher temperature (say 30° C.) again, for five minutes. A second set of responses was now taken. In this way observations were made with each specimen till the temperature at which response almost or altogether ceased was reached. I give below a table of results obtained with six specimens of radish, from which it would appear that response begins to be abolished in these cases at temperatures varying from 53° to 55° C.
Table showing Effect of High Temperature in Abolishing Response
| Temperature | Galvanometric response (100 dns. = ·07 V.) | ||
|---|---|---|---|
| (1) { | 17° C | 70 | dns. |
| 53° | 4 | " | |
| (2) { | 17° | 160 | " |
| 53° | 1 | " | |
| (3) { | 17° | 100 | " |
| 50° | 2 | " | |
| (4) { | 17° | 80 | " |
| 55° | 0 | " | |
| (5) { | 17° | 40 | " |
| 60° | 0 | " | |
| (6) { | 17° | 60 | " |
| 55° | 0 | " | |
