THE PRAIRIES OF THE PACIFIC NORTHWEST. 33 



roots reach a depth of 4 feet 10 inches, although on an average 4 feet 2 inches 

 was the greatest depth attained. 



Festuca ovina mgrata. — The blue bunchgrass ranks in importance with 

 Agropijrum on the well-developed high prairies west of the foothills of the 

 Bitterroot Mountains between Spokane, Washington, and Lewiston, Idaho. 

 Because of its abundance the very appropriate name Palouse (Fr. pelouse, a 

 land clothed with a short, thick growth of herbage) was early apphed to this 

 region. The whole plant dries out considerably by the middle of July, but the 

 autumn rains revive it and it is green throughout the rest of the year. 



Festuca ovina has a great ma,ss of jet-black roots which occupy the soil 

 thoroughly from the surface to a depth of about 18 inches, below which depth 

 relatively few roots extend. None of the roots are over 1 mm. in diameter. 

 They branch profusely to the third order mostly, and the laterals are usually 

 less than an inch in length. This branching continues to the very tip, and 

 there the laterals are usually longer. The longest root found was 3 feet 3 

 inches, and the average length was 2 feet for the deepest roots, but the great 

 bulk of these roots were less than 18 inches long. 



Pea sandbergii. — This species grows in small tufts, usually only from 0.5 

 to 1.5 inches wide, puts out new roots when the fall rains begin, grows through- 

 out the winter and spring, and evades drought by flowering late in May or in 

 early June and remaining dormant the rest of the growing season. 



Poa has smaller roots than Festuca; they are more profusely branched, 

 and the fine, short laterals are more numerous, smaller, and much more 

 branched. The creamy- white roots spread laterally 3 to 5 inches and occupy 

 thoroughly the first few inches of soil, relatively few extending below a depth 

 of 8 inches, and none was found beyond 13 inches. The root branches are 

 longer and more numerous at the tip than are those of Festuca. The average 

 maximum depth was found to be 10 inches. 



Koeleria cristata. — This is also a dominant bunchgrass on the prairies of 

 eastern Washington. It flowers in late June or early July, and hke Poa 

 remains dormant until revived by the autumn rains. The roots resemble 

 those of Agropijrum, but taper faster and have finer laterals which branch 

 mostly to the third order. These laterals, like those of the shallow-rooted 

 Poa, are more numerous than in Agropyrum. The deepest root found was at 

 28 inches, and 15 inches was determined as the average maximum depth. 

 The shallow root habit of the three last species as compared with the deeper- 

 root habit of Agropyrum and certain dicotyledonous plants is shown graph- 

 ically in figures 6 and 7. 



THE ROOT SYSTEMS OF OTHER PRAIRIE SPECIES. 



Since the root systems of 21 of the most important non-grassy 

 prairie species have been described in detail in a former publication 

 (1915), it will be necessary here only to present a summary statement, 

 so that it may be possible to compare their root systems directly with 

 the plants of the eastern prairies and later with those of the plains. 

 Such a comparison will help us to more clearly evaluate the response 

 to the conditions under which the several plant communities grow. 



Lupinus ornatus. — This plant and L. leucophyllus are the two species of 

 lupines most widely distributed on the high prairies of eastern Washington. 

 Both form extensive summer societies, the former on the drier slopes and 

 ridges, the latter on moist hillsides and in the valleys. Several of the 24 root 



