PRAIRIE PLANTS OF SOUTHEASTERN WASHINGTON 



287 



trated to depths of 6 feet and 9 inches; 7 feet and 5 inches; and 7 

 feet and 5 inches respectively. The average depth was found to 

 be 5 feet and 1.8 inches. Twelve plants on a northeast slope 

 gave an average root depth of 4 feet and 11.2 inches, while 17 on 

 a northwest slope reached an average depth of 5 feet and 4.3 inches. 





Fig. 17 Fig. 18 



Fig. 17. This shows the numerous roots sent out from the corymb of Hieracium 

 scouleri. The total length of only one root is shown. 



Fig. 18. Eriogonum heracleoides from the rim-rock. A single branch of the 

 large mat is shown just above the meter stick. Note the adventitious roots. 

 Only a small part of the complete root-system is shown in the figure. • 



Eriogonum heracleoides (Fig. 18) 



This plant seldom occurs except on the very driest ridges of 

 high basaltic prairies, but is a very important ecological species 

 upon the rim-rock and in the bunchgrass association. The 

 great mats often cover an area of 2-3.5 square feet and the 

 prostrate branches with their adventitious roots serve both to 



