THE PRAIRIES. 



17 



Ceanothus ovatus.— This low shrub, with its many stems 1.5 to 3 feet high, 

 is quite common on prairies, especially in the eastern part of Nebraska. It 

 also occurs widely throughout the sandhills westward, and on the loess hill, 

 where the following specimen was excavated, it is rather abimdant. 



The plant examined was 13 yeare old. It had 14 stems arising from the 

 enlarged crown. The woody tap-root was 1.5 inches in diameter. At a depth 

 of 8 inches it gave off a large lateral and 2 inches below another which was 

 equal in diameter to the tap (2 cm.) at this depth. While the first lateral and 

 the tap pm-sued a rather vertically downward course (being, like all of the 

 roots, very much curved and twisted, so that at a depth of 11 feet the tap wa^ 

 only 15 inches from a vertical line with the top), the second lateral at a depth 

 of 7 feet was 50 inches from this vertical line (plate 12, a). Also, numerous 

 small, repeatedly branching laterals and a few larger ones (6 mm. in diameter) 

 came off in the surface foot of soil and ran in rather horizontal directions for a 

 distance of 3 to 5 feet. In addition to these surface absorbing roots, both 

 short and long laterals were given off at intervals at all depths, the whole 

 root branching and rebranching freely. While some of the roots branched 

 coarsely and ended abruptly, others formed a most delicate mass of absorbing 

 rootlets. As a whole, the root system is well-branched, but some of the roots 

 at a depth of 10 or 11 feet (and where they were only 2 or 3 mm. in diameter) 

 ran 2 or 3 feet without giving off any branches. Numerous roots occurred 

 at a depth of 8 feet, several reached 12 feet, and the longest one was traced to 

 a depth of 14.5 feet, where it was still 1 mm. in diameter and giving off fre- 

 quent threadlike laterals. The older parts of the root are woody and extremely 

 hard. Deeper down they lose their toughness and become very brittle, while 

 the smaller roots are again fairly tough. All parts of the root are character- 

 ized by a reddish-brown color, all but the oldest being more or less streaked 

 with white. They reveal a reddish color upon removal of the bark, this color 

 also extending into parts of the wood. 



Amorpha canescens.— A 7-year-old specimen, which is very representative 

 of others examined, was excavated near the foot of the loess hill. It gave off 

 11 large woody roots, 8 to 14 mm. in diameter, from the knotty crown. These 

 ran off at various angles from almost parallel with the hillside to almost 

 vertically downward (plate 12, b) where the roots are somewhat grouped, 

 owing to the fact that the background was only 5 feet wide. These have 

 very few surface laterals, but those that do occur are well-branched. In the 

 surface 2 to 4 feet of soil relatively little absorption takes place. Andropogon 

 scoparius and other grasses frequently grow vigorously between these spr^d- 

 ing Amorpha roots and doubtless suffer little competition for water. The 

 roots taper uniformly and at a depth of 3 feet are often still 7 mm. m diam- 

 eter. They frequently pursue a rather tortuous course and branch in a way 

 more or less dichotomous. Rebranching gives rise to many small laterals 

 only 1 to 4 mm. in diameter, which pursue a vertically downward course for 

 many feet, giving off very few branches and tapering only slightly. Even the 

 tips are usually poorly branched. The lateral spread of the roots is remark- 

 able. One lateral reached a depth of 12 feet 10 inches and a horizontal dis- 

 tance of 4 feet from the base of the crown. Another was also 4 feet from a 

 vertical line with the crown at a depth of 12 feet 2 inches and about 5 feet from 

 the end of the first lateral. Similar conditions obtained on the other sides of 

 the plant, so that a very large area of soil was penetrated by the roots of a 

 single plant. 



Small nodules only 1 mm. in diameter occur as deep as 10 or 12 feet. On 

 the higher slope one plant was noted that showed much-branched root-tips 



