In radishes response disappeared completely at 55° C., but with celery, heated in the manner described, I could not obtain its entire abolition at 60° C. or even higher. A noticeable circumstance, however, was the prolongation of the period of recovery at these high temperatures. I soon understood the reason of this apparent anomaly. The method adopted in the present case was that of dry heating, whereas the previous experiments had been carried on by the use of hot water. It is well known that one can stand a temperature of 100° C. without ill effects in the hot-air chamber of a Turkish bath, while immersion in water at 100° C. would be fatal.
In order to find out whether subjection to hot water would kill the celery-stalk, I took it out and placed it for five minutes in water at 55° C. This, as will be seen from the record taken afterwards, effectively killed the plant ([fig. 38], w).
Fig. 39.—Effect of Rising and Falling Temperature on the Response Of Scotch Kale
Increased sensitiveness as after-effect of temperature variation.—A very curious effect of temperature variation is the marked increase of sensitiveness which often appears as its after-effect. I noticed this first in a series of observations where records were taken during the rise of temperature and continued while the temperature was falling ([fig. 39]). The temperature was adjusted by electric heating. It was found that the responses were markedly enhanced during cooling, as compared with responses given at the same temperatures while warming (see table). Temperature variation thus seems to have a stimulating effect on response, by increasing molecular mobility in some way. The second record ([fig. 40]) shows the variation of response in Eucharis lily (1) during the rise, and (2) during the fall of temperature. [Fig. 41] gives a curve of variation of response during the rise and fall of temperature.
Table showing the Variation of Response in Scotch Kale
during the Rise and Fall of Temperature
| Temperature | ↓ | Response [Temperature falling] | Response [Temperature rising] | ↑ | |||
|---|---|---|---|---|---|---|---|
| 19° C. | 47 | dns. | — | ||||
| 25° " | 24 | " | — | ||||
| 30° " | 11 | " | 23 | dns. | |||
| 50° " | 8 | " | 16 | " | |||
| 70° " | 7 | " | — | ||||
| → | |||||||
