8 



In order to secure uniform soil conditions in ^'m 

 various cultures, it was necessary not only that the soil 

 should be of the same character in all of them but also that 

 it should be brought into the same physical condition for the 

 beginning of all cultures, furthermore, it was desirable that 

 this physical condition be such that it would be retained 

 during the growth periods of the plants. To put the soil into 

 a state of aggregation to be least altered by varying wee,ther 

 conditions (especially heavy rains which "oack the vsoil more 

 or less) it was saturated with water immediately after being 

 put into the pots. This was accomplished by plunging the 

 filled pots into a bucket of water and allowing them to remain 

 submerged until air bubbles ceased to rise. The pots were 

 then allowed to drain. 



The soil moisture .in the cultures was maintained always 

 above a certain minimum by means of auto-irri gators. This 



^Livingston, B. 3., A n.ethod for controlling plant mois- 

 ture. Plant V/orld. 11: 39-40.1908. 



device, as here used, consisted of two cylindrical porous 

 clay Gu-os (o'' the regular form supplied by the Plant Y/orld) 

 connected with each other and with a water reservcir by glass 

 tubes in the -'''-> r-r^ of an inverted J. The cups were placed ver- 

 tically in th oot, their rubber- stoppered tops level with the 

 soil surface, and Tvere so arranged as to supply w,- ter to the 

 soil against a pressure of 35 cm., or somewhat raor-- , of a 

 water column. The moistxire content of the soil was thus 

 maintained so that it was never less than about 10 to 13 



