76 



W. R. MOLLER-STOLL AND G. LERCH 



the relations, as shown by Fig. 4, were partly inverted here. From the 

 dried-out basal soil, water could be moved upward to such an extent that 

 soil moisture in the upper tubes decreased but very shghtly. From the 

 moist soil, fmally, so great a quantity of water was transferred into the 

 apical containers that soil moisture increased here continuously in spite of 

 the transpiration from the test plants. When the experiment was stopped 

 after 8 days no test plants showed any signs of wilting. 



(d) Low Temperature 



During the tests described so far, the temperature gradient was estabhshed 

 by leaving the top of the test set-up in the temperature of the surrounding 

 air (20-30°C), and by heating the bottom of the lower tubes up to 45°C. 

 Thus the whole set-up was subject to relatively high temperatures, although 

 the temperature gradient itself did not exceed io-i2°C. The same tempera- 

 ture difference, however, could be maintained by omitting the water bath 

 and merely enclosing the top of the apical tubes in an ice jacket. Tempera- 

 tures within the test set-up ranged then from 5°C at the top to 1 5°C at the 

 bottom. 



Figure 6 shows the results of these tests. In principle there is no change to 

 the previous evidence. Vapour moved upward, condensed there, and was 



I 



(8-3%) 



6 days 



Fig. 6. Ecological effect of a moderate temperature gradient at low temperature on 

 vapour movement and condensation in soil with a rooted plant. For key, see Fig. 3- 

 Vapour tension of air: 63-3 %. 



