74 



W. R. MOLLER-STOLL AND G. LERCH 



to a moderate temperature gradient of about 8°C. Therefore, the lower 

 soil columns of the control sets also lost water in this case. 



days 



Fig. 4. Ecological effect of vapour movement due to a temperature gradient m soils, 

 with rooted plants, of different moisture. For key, see Fig. 3. Vapour tension of 

 air: 58%. 



From the dry basal soil less vapour moved upward than from the moist 

 soil. The control plants above the dry basal soil thus wilted on the sixth 

 day again, those with a moist soil in their basal tubes did so one day later 



(Fig- 5). 



