ROOT SYSTEMS 



31 



growth in the early summer months, and lie dormant 

 through the droughts of July and August. 



Contrasted with this community is the prairie of the 

 Pacific Northwest (Washington) with a different floristic 

 composition, characteristic plants being Sicversia ciliata, 

 Wiethia ampkxicaulis, Liipinus leiicophyllus , Lupmus ornatus, 

 Poa sandbergii, LeptoUeriia miiltifida, Agvopynim spicatum 

 (Fig. 2). There are three grasses with a root system con- 

 fined to the first 18 in. of soil ; these, again, lie dormant 



f«et 



Fig. 2, — Root systems of typical plants of the Washington prairies ; 

 s, Sieversta ciliata ; w, Wiethia amplexicatilis ; II, Lupi?ius leucophylliis ; 

 lo, Lupinus ornatus; p, Poa sandbergii; e, Leptotcenia midtifida ; 

 a, Agropyriim spicatum. (From Weaver.) 



through the summer months. The remainder of the species 

 examined had root systems of medium depth from 4 to 6 ft., 

 only one or two penetrating as deeply as 10 ft. The rainfall 

 in this region is about 20 in., and occurs chiefly in the 

 winter months. The soil is a friable, dark brown, silt loam 

 originating from the decomposed underlying basalt, and is 

 many feet deep. It absorbs water during the winter and 

 acts as a reservoir ; during the growing season it is gradually 



