Page:Life Movements in Plants.djvu/57

Rh plant completely immersed under water shows once more that transpiration has little to do with the diurnal movement.

The diurnal rhythm of up and down movement in the particular specimen Basella had become established under the daily variation of temperature. I now attempted to reverse this rhythm by artificial variation of temperature. The plant was placed in water in a rectangular metallic vessel which was placed within a second outer vessel. The plant could thus be subjected, without any mechanical disturbance, to variation of temperature, by circulating warm or cold water in the outer vessel. In order to reverse the natural rhythm I subjected the plant to the action of falling temperature at the "turning" point at 7, at a time when the plant would have undergone a down-movement under the daily rise of temperature. Conversely the plant was subjected to the action of rising temperature at the second "turning" point at 1, when the movement under diurnal fall of temperature would have been one of erection.

Effect of fall of temperature: Experiment 8.—As stated before the experiment was carried out in the morning; ice cold water was circulated in the outer chamber, the fall of temperature was in this case sudden, and there was an almost immediate responsive movement. This appeared anomalous, since the latent period of response to slow variation of temperature was found from the diurnal curve to be as long as 50 minutes.

As a result of further investigations I found that variation of temperature produces two different effects which may he distinguished as transient and persistent. Sudden variation of temperature affects the superficial tissue, and gives rise