Jan. 2. 1920 Relation of Moisture in Substrata to Salt Balance 359 



conducted simultaneously. The three series were alike in every respect 

 except in the quantity of solution which was diffused as a film over the 

 solid sand particles. All the cultures of the same series received the 

 same amount of solution and were kept at approximately the same 

 moisture content; but the cultures of the different series received different 

 amounts of solution, so that the moisture content throughout each 

 series was different from that of the other two series. Thus, corresponding 

 cultures of the three different series received different amounts of the 

 same solution, the differences in their moisture content being regulated 

 by adding more or less solution as the case required. 



All the cultures of one series were prepared with a moisture content 

 of approximately 40 per cent of the water-holding capacity of the sand, 

 all the cultures of another series with a moisture content of 60 per cent, 

 and those of the third series with a moisture content of 80 per cent. 

 These values were chosen as the result of preliminary tests which showed 

 that a moisture content of 60 per cent of the water-retaining capacity 

 of the sand used was well within the range for optimum growth, while the 

 first and third values selected were considerably below and above this 

 range. 



The substratum used in these cultures consisted of white seashore 

 sand which was thoroughly washed with tap water followed several 

 times with distilled water. This sand had a water-retaining capacity 

 of 25 per cent on the dry- weight basis (average of six tests) determined 

 according to the method of Hilgard (7, p. zog). Thus the moisture 

 contents of the three different series were 10 per cent, 15 per cent, and 20 

 per cent, respectively, based on the weight of the air-dry sand. 



Half-gallon glazed earthenware pots were used as culture vessels. 

 Each pot held 2,500 gm. of dry sand when filled to within several cen- 

 timeters of the top. To prepare the sand in each pot for the planting 

 of the seedlings, a sufficient amount of nutrient solution was poured into 

 the sand to bring it almost to the point of saturation. Five carefully 

 selected seedlings of spring wheat o^f the Marquis variety were then 

 transplanted to the sand culture from a germinating net, after which the 

 culture was flooded until free nutrient solution appeared over the surface 

 of the sand to the depth of i cm. or more, thus fixing the seedlings in place 

 and at the same time leveling the surface of the sand. This initial 

 application required 750 cc. of solution for each culture. The excess 

 solution was then withdrawn and the sand reduced to the desired moisture 

 content by a method {14) which had previously been described and which 

 is a modification of the method devised by McCall {8) for the renewal 

 of solutions in sand cultures. 



The solutions were renewed at 3-day intervals. After each culture 

 had been restored to its original weight by the addition of distilled water, 

 as much as possible of the old solution was withdrawn, and the culture 

 was flooded with 500 cc. of new solution. The culture was then restored 



