i6 



BOTANICAL GAZETTE 



[JULY 



B. The surface forces of soils. — i. The Oswego silt loam. — 

 A number of tests were made with the subsoil of the Oswego silt 

 loam, the results of 4 of which are shown in table V. The air-dry 

 soil apparently holds its moisture with about the same force as do 

 air-dry seeds, a result one might expect, since both are in moisture 

 equilibrium with the same atmosphere at air-dry. 



TABLE V 



Relation of soil moisture in subsoil of Oswego silt loam to water intake 

 by seeds or Xanthium pcnnsylvanicum 



Soil H,0 



. percentage of absolute 



weight 



Intake H,0 

 in percentage of 

 air-dry weight 



95 (air-dry). 

 IS 



'5 (air-dry). 



0.38 



I-S8 

 3-73 

 6.16 

 10.76 

 15-79 

 21.36 

 28.61 

 33-86 

 45-iS 

 4931 



-o.S3 

 + 1.06 

 3-68 

 6.47 

 10.82 

 15.81 

 21. 11 

 32.60 

 4I.9S 

 47.26 

 50.00 



As soil moisture is increased, the moisture intake by the seeds 

 increases at a much more rapid rate, until the approaching satura- 

 tion of the seed begins to cut down the absorption rate. This 

 happens as the soil moisture approaches the wilting coefficient. 

 Reference to rig. 4 will make the relationship of soil moisture 

 content to seed intake clear. 



