1920] PALMER, LIGNEOUS FLORA OF THE STAKED PLAINS 97 



than a tall shrub, often sending up a number of stems from burned-oflf 

 stumps. In more protected situations it becomes arborescent, the largest 

 specimens observed being about 12 or 15 metres in height and 4 or 5 deci- 

 metres in trunk diameter. It is rather abundant in the same zones as the 



last species. 



Ephedra Torreyana Wats. 



This interesting shrub is usually found near the summit of the canyon 

 walls in the Upper Cap-rock zone. Its naked, Equisetum-like stems are 

 much branched and present a very curious appearance. It was also found 

 near Channing, in Hartley County. 



Populus texana Sarg. 



One of the commonest and largest tree along the margins of the river, in 

 the deep side canyons and under the protection of cliffs is the Cottonwood, 

 which has recently been described by Professor Sargent under this name. 

 While not attaining the large size of some of the other Cottonwoods, speci- 

 mens 20 metres high and 75 or 80 centimetres in trunk diameter are fre- 

 quent. The trunks are often bent and branched from near the ground. 

 This species was observed in Nolan, Garza, Randall, Armstrong and Hemp- 

 hill Counties, and doubtless occurs elsewhere in canyons of the Staked 

 Plains and along the northern border of the Edwards Plateau and probably 

 extends into southwestern Oklahoma. 

 Salix amygdaloides Anders. 



A common Willow in the River-bank zone, both in the canyons and in 

 more open situations wherever there are running streams or pools, 

 sometimes 10 or 12 metres high. 

 Salix exigua var. stenophylla (Rydb.) Schneid. 



A shrub or slender tree found rarely in the River-bank zone and watered 

 side canyons. Much more abundant along pool and stream margins in 

 more open situations on the plains. 

 Quercus Mohriana Rydb. 



tree 



Lower 



Usu- 



ally a shrub from one to three metres high, but in the protection of cliffs and 

 in deep side canyons sometimes becomes a tree seven or eight metres high, 

 with thick, rough, pale bark and a low conical crown. The leaves are 

 quite variable in size and shape. 

 CelHs laevigata var. texana Sarg. 



A small tree common in the Canyon-floor and River-bank zones, and less 



abundant in the higher zones of the canyon walls. 

 Mahonia trifoliata Moric. 



This curious and rather pretty shrub of the arid Southwest, called Ar- 



Mexicans, is occasionally found in the Lo 



zone. 



Morus microphylla Buckl. 



The Mexican Mulberry, a typical tree of the Edwards Plateau, appears 

 to be rather rare except along the southern border in the Staked Plains. 



seen 



