THE PRAIRIES. 



13 



Shantz lists Grindelia as one of the plants commonly found in the short- 

 grass association of Colorado. It usually indicates disturbed conditions and 

 is especially abundant during wet years. It appears that its root system 

 must be greatly modified under these conditions where the soil is only rarely 

 wet below a foot or two. Indeed, it seems to thrive so well and under such 

 varied conditions that it is a conspicuous weed throughout many of the 

 Western States. It is likely that the great plasticity of its root system makes 

 this wide distribution possible. 



Glycyrrhiza lepidota. — This characteristic legume has much-branched 

 rhizomes several feet long and a deep, fleshy tap-root. In the several speci- 

 mens examined the tap-root varied from 0.5 to 2 inches in diameter. From 

 the multicipital crown as many as 15 to 20 stems may arise. Just below the 

 surface soil small laterals, a few millimeters to a centimeter in diameter, are 

 often given off, in a more or less horizontal direction. These often turn down 

 abruptly. At a depth of 1 to 3 feet the tap frequently breaks into many 

 strong branches with a lateral spread of 2 or 3 feet from the base of the crown. 

 They run off rather obliquely from the main root (plate 8, b) giving rise to 

 numerous long branches. These tertiary roots are usually only 2 to 5 mm. in 

 diameter and rebranch poorly, a lack of small, absorbing roots being quite 

 characteristic. The deeper soils (8 to 10 feet) are thus well filled with small, 

 vertically descending, poorly branched roots, 1 to 3 mm. in diameter. Like 

 the older roots, these are of a light-brown color and fleshy but quite firm. 

 They shrink rapidly upon exposure to the air. At 10 to 12 feet, where these 

 rootlets entered the jointed clay-loess soil, they branched rather profusely. 

 The roots of several plants were traced to depths of 11 or 12 feet. One of the 

 larger ones was still 2 mm. in diameter at this depth and probably penetrated 

 several feet deeper. The odor is very characteristic. 



Astragalus crassicarpus. — During May 1918, a large trench was dug on a 

 west hillside at Belmont, about 45 feet from a wet Spartina cynosuroides zone 

 in the valley. The surface foot of good loam soil gave way to about 3 feet of 

 exceedingly hard joint clay, in which roots (and especially those of grasses) 

 frequently followed the joints and branched largely (locally) in one plane. 

 The deeper soil became wetter and also somewhat sandy, but very gummy 

 and sticky. The water table was reached at about 7 feet. From this trench 

 Astragalus, two species of Psoralea, and Baptisia were excavated. 



Astragalus crassicarpus forms extensive societies in the early spring. A 

 group of 3 younger ground-plums was first examined ; the plants were very 

 similar in size, root diameter, branching, and depth. One (shown in plate 

 9, b) had a pronounced tap-root with a diameter of 1 cm. and ran almost 

 vertically downward to a depth of 6 feet, giving off a number of horizontal 

 branches, 1 to 2 mm. in diameter, near the surface, and extending laterally 

 only a few inches before turning downward. Other smaller laterals from 0.5 

 mm. to those hairlike in diameter occurred sparingly and at intervals of about 

 1 cm. or less to a depth of 4 feet. Most of these branches were less than a 

 centimeter in length. Below 4 feet, in the softer, wetter soil, the branches 

 became more pronounced, being densely covered with root-hairs and often 

 branching in two planes. However, none of these branches exceeded an inch 

 in length. The tip of the tap (as well as the tips of the laterals, which reached 

 depths only about half as great as the former) was no better branched than 

 was the last 2 or 3 feet of the root. There is a very noticeable tendency for 

 the roots to follow the crevices in the joints of the clay. 



An older plant had a strong tap-root with a diameter of 1 cm. At a depth 

 of 2 cm. it gave off a strong lateral 5 mm. in diameter and at about the same 



