MODEL TESTS OF VAPOUR MOVEMENT IN SOIL 



67 



The lower end of the basal tube was tightly closed by a rubber plug in 

 order to prevent water from invading from outdoors. The lower end of the 

 apical tube was closed by a piece of fine Perlon gauze. 



Fig. I. Test equipment, (a) with test plants, (b) without test plants, apical containers 

 enclosed in ice jacket. Key : (i) Test plant, (2) Petroleum jelly- vaseUne sealing, (3) Glass 

 wall of the apical tube, (3a) Apical soil column ( = 'top'), (4) Perlon diaphragm, (5) Fold- 

 ed rubber hose, (6) Strip of plaster, (7) Glass wall of the basal tube, (7a) Basal soil column 

 (= 'base'), (8) Rubber plugs, (9) Thermometers, (10) Hollow cylindrical ice containers. 



Both containers were filled with fme soil (loamy sand) as firmly as 

 possible. In the apical tubes seedlings of Pisum sativum ('Maiperle') were 

 grown in the usual manner until their root systems had thoroughly 

 permeated the small soil column available. 



At the beginning of each test the soil surface in the apical tube was sealed 



