152 



T. G. YUNCKER 



5 mm. glass tube was inserted to a depth of about 5 cm. through 

 the hole in the bottom of the flower pot. The glass tube was left 

 long enough to extend above the level of the top of the potometer. 

 This tube was used for watering. Another glass tube 10 mm. in 

 diameter was placed with one end in the gravel layer and the 

 other extending a few centimeters out of the potometer. This 

 latter tube was for the purpose of aeration. The loam soil was 

 then added to within 5 cm. of the potometer top and jarred down 

 sUghtly to render the soil mass homogenous (see fig. 1). 



Starting the potometers and establishing initial moisture content. 

 The corn plants were started in flats of loam soil. When they 



Fig. 1. Diagram of potometer. 1, plant; 2, watering tube; 3, aerating tube J 

 4, paper collar; 5, wax seal; 6, glazed crock; 7, flower pot. 



were approximately 2 inches high they were transplanted, five 

 to a potometer, the weaklings being discarded. Four plants were 

 run in each potometer, but five gave an opportunity of discard- 

 ing a weak one before sealing. After transplanting, the plants 

 were watered by pouring equal amounts of water into each po- 

 tometer by means of the tube for that purpose. As soon as the 

 seedlings were making a good growth they were allowed to go 

 without watering until the plants showed signs of wilting. This 

 was taken as the lowest moisture content at which they would 

 grow. 25 cc. of water was then added to each potometer in 

 order that the plants would be slightly above the wilting point. 

 Trials were then made with similar amounts of soil and it was 

 found that 500 cc. of water would render the amount of soil con- 



