190 PAUL C. STAND LEY 



the hillsides the scrub-oak gives place to sagebrush (Artemisia 

 tridentata) and rabbit-brush (Chrysothamnus graveolens, C. vaseyi, 

 and C. parryi), but these shrubs occur only sparsely and are 

 nowhere so dense as one often finds them in typical Upper 

 Sonoran areas. Some of the characteristic herbs are Amaran- 

 thus powellii, A. pubescens, and A. blitoides, Pentstemon xylus, 

 Chenopodium leptophyllum,Eriogonum cernuum and!?, racemosum, 

 Gutierrezia tenuis, Aster crassulus, Stanleya glauca, Helianthus 

 annuus, Hymenoxys floribunda, Grindelia pinnatijida, Sideran- 

 thus gracilis, Bouteloua gracilis and B. prostrata, Agropyron 

 smithii, Atriplex rosea, Boebera papposa, Madia glomerata, 

 Anogra coronopifolia, Artemisia dracunculoides , Ratibida colum- 

 naris, and Senecio multicapitatus. Nearly all of these are Upper 

 Sonoran plants, but associated with them are fully as many 

 others that are typical of the Transition Zone. 



Where the valley of the Brazos widens there are broad flats, 

 sometimes on one and sometimes on both sides of the stream. 

 When the winter snows are melting the water cuts new channels 

 across this flood plain, where it is not protected by cultivation, 

 depositing soil in some places and in others washing it away 

 and leaving beds of rounded stones or gravel. This area is 

 overgrown with mountain cottonwoods, which reproduce rapidly 

 and often reach a large size. Cedars (Juniperus scopulorum) 

 grow with them in places, usually in thick shade, where they 

 seem out of place. Probably cedars were more abundant 

 formerly in the valley and on the "hillsides, before they were cut 

 for firewood. There are scattered shrubs of sagebrush and 

 rabbit-brush here, as well as on the hills. 



The herbaceous plants of the flood plain are much like those 

 of the hillsides, except that there is a greater proportion of 

 typical Transition plants. Clematis ligusticifolia climbs over 

 many of the cottonwoods. Large areas are covered with a 

 thick growth of Antennaria microphylla and a white-flowered 

 perennial lupine. Many species of grasses abound, but the 

 number of individuals is smaller than on the hillsides. On 

 gravel banks and in moist soil common plants are Argentina 

 anserina, Halerpestes cymbalaria, Sideranthus gracilis, Aster 



