THE PRAIRIES OF THE PACIFIC NORTHWEST. 35 



systems examined reached depths of over 10 feet; because of the devious 

 course they pursue, the tap is frequently much longer. Indeed, one was 

 found to have a length of nearly 13 feet. The abundant laterals, their wide 

 spread, and the clusters of terminal branches, together with the root nodules, 

 are shown in figure 7. 



Lupinus leucophyllus. — This lupine has a much larger transpiring surface 

 but a much smaller absorbing surface than L. ornatus, which it resembles in 

 having a well-developed tap-root, usually with several laterals, all of which 

 are branched to the third and fourth order. However, the root system is 

 much less extensive than that of L. ornatus ; its average depth is only about 5 

 feet (fig. 7). 



Astragalus arrectus. — This legume forms marked estival societies, the 

 plants drjdng up during the first week in July. It has a strongly developed 

 tap-root, which usually pursues a course directly downward and sends out 

 many strong laterals at various depths. These laterals are fairly wide- 

 spreading and profusely branched to the tip. They reach depths of 4 or 5 

 feet (fig.' 8). 



Balsamorhiza sagittata. — The balsam-root is a dominant in the high 

 prairies of eastern Washington. Its abundance, size, and duration all unite to 

 make it a very important species ecologically. From the short, thick, mul- 

 ticipital stem the new leaves appear in April. By the first of May the plant 

 is often in full bloom, forming societies which are very conspicuous, even after 

 the whole aerial part has dried up. Twenty-five root systems were excavated 

 and examined. Balsamorhiza has a tap-root sometimes reaching a diameter 

 of 4 inches and an extreme depth of 8 feet 10 inches. The laterals seldom 

 come ofi" in the first 6 inches of soil, but numerous strong laterals occur below 

 this, sometimes 1 inch or more in diameter, and these often run rather hori- 

 zontally for 2 or 3 feet before they turn downward. They may ultimately 

 reach depths of 5 feet or more. The lateral branching is profuse, and in all 

 directions the soil is laid hold upon. Sometimes the tap sphts up into nearly 

 equal parts at a depth of a few feet. The tip of the tap-root is often dead, and 

 if alive is never much branched. The older part of the root especially is 

 covered with a bark furrowed sometimes 0.5 inch deep. The average root 

 depth was found to be 5.5 feet (fig. 6). 



Geranium viscosissimum. — This subdominant forms extensive societies in 

 the estival aspect. It has a well-developed tap-root which may reach 3 inches 

 in diameter. The tap sends off many laterals, both large and small, at all 

 levels, all of which may branch profusely to the fifth order. The larger laterals 

 usually run off in a horizontal direction, sometimes for nearly 3 feet before 

 turning downward. The end of the tap-root is either unbranched or branched 

 but little, and is often dead. Hard soil seems to be a marked limiting factor 

 to root growth, and under this condition, especially, the usual very irregular 

 course of descent is greatly emphasized. Twenty-four root systems were 

 examined. While one plant penetrated to 9.5 feet, the average depth was 

 found to be 5.5 feet (fig. 6). 



Wyethia amplexicaulis. — This large, rather coarse plant is at home on 

 moist hillsides and especially in valleys, where it forms extensive estival 

 societies. It has a fleshy tap-root, which sometimes measures 9 inches in 

 circumference and may reach a depth of 6 feet 5 inches. It usually has several 

 strong laterals which come off from 8 inches to 3 feet in depth, and may run 

 out in a somewhat horizontal direction for 3 or 4 feet from the main root. 

 Often at a depth of 1 to 3 feet the whole tap breaks up into 2 to 5 nearly equal 



