THE PRAIRIES. 



21 



prairies of southeastern Washington, where during 1914 the water- 

 content to a depth of 4 feet was reduced to the non-available point 

 (Weaver, 1915:233-235). 



The available water-content in the loess soils supporting the sub- 

 climax prairie vegetation was not only higher but much more con- 

 stant. These data are shown in tables 4 and 5. Here also are included 

 determinations from an adjacent thicket of Corylus americana. A 

 comparison of these results is made on page 30. 



Table 4. — Available water-content in prairie and shrub communities near Peru, Nebraska, 



during April to September 1917 and May 1918} 



The minus sign indicates water non-available for plant growth. 



1 The writer is indebted to Prof. F. C. Jean for the major portion of the data in these tables. 



The greater water-content of these mellow loess soils compared with 

 those of the prairie near Lincoln gives us a clue to the much more 

 luxuriant growth of certain prairie and shrub species. There is also a 

 great difference in depth of root-penetration, plants hke Andropogon 

 furcaius and Brauneria -pallida being much deeper-rooted in loess soil. 



However, vegetation is not only an expression of present conditions, 

 but also to a greater extent a record of conditions that have obtained 

 during a period of years, and the record is not likely to be altered 

 greatly in a year or two in which conditions may depart from the 

 normal. The preceding pages show that many prairie plants absorb 

 moisture well beyond a depth of 5 feet, while soil-moisture extends 

 many feet beyond the greatest root depth. In excavating root systems, 

 during September to December 1917, the soil below 5 feet was found 

 almost invariably to be quite moist. Some of the root systems were 

 excavated on bench-lands in the Salt Creek basin, where the alluvial 

 soils are somewhat different from those described. Such differences 

 were noted in discussing these species. 



