98 JOURNAL OF THE ARNOLD ARBORETUM [vol. n 



Prunus angustifolia Marsh. 



Found occasionally in small thickets in the Canyon-floor and River-bank 

 zones. 

 Prunus virginiana var. demissa (Nutt.) Torr. 



Growing in deep watered side canyons and under the protection of bluffs 

 near water. 

 Cercocarpiis argenteus Rydl. 



A common and typical shrub of the Upper Cap-rock zone. Seldom more 

 than two or three metres high. 

 Proaopis glandulosa Torr. 



The Mesquite is one of the commonest ligneous plants in the canyon. It 

 is most abundant in the Canyon-floor zone, where it becomes a tree, some- 

 times ten metres or more in height, but it is also found along the margins of 

 the river and along tlie sides of the canyon to the upper plains. In the last- 

 named situation it is struggling to maintain and extend a precarious foot- 

 hold on the open, wind-swept surface, but it seldom becomes more than a 

 shrub two or three metres in height. 

 Mimosa horealis Gray. 



The low, thorny Cat's Claw grows in similar situations to the Mesquite 

 but is perhaps commonest in the broken, rocky ground below the lower cap- 

 rock, 

 Dalca formosa Gray. 



This diminutive shrub is rather common in rocky ground of the Lower 

 Cap-rock zone and is less frequent in the zones above and below. 

 Gleditsia triacanthos L. 



There is a small grove of Honey Locust trees in the Club House grounds 

 near Canyon City and it is said to occur sparingly elsewhere in the upper 

 part of the canyon. The trees seen are of small size for the species, averag- 

 ing, perhaps, eight or ten metres in height. It appears to be absent lower 

 down in the canyon. 

 Amorpha fndicosa L, 



Rather frequent in the River-bank zone and in low places of the Canyon- 

 floor zone. 

 Amorpha canescens Pursh. 



Collected along the banks of a small ravine above the upper cap-rock. 

 Apparently not common. 

 Glossopetalon spinescens Gray. 



This is one of the most interesting shrubs found in the canyon from the 

 standpoint of plant distribution. On the Edwards Plateau I observed it 

 only along the western and southern borders in Uvalde County and in the 

 Devils River region, where it seems to have come in from the Trans-Pecos 

 country. In the Paloduro Canyon it grows on calcareous banks of the 

 Upper Cap-rock zone. It was seen near Canyon City, in Randall County, 

 and south of Claude, in Armstrong County. 

 Ribes aureum Pursh. 



In deep canyons and along protecting cliffs in the Upper and Lower Cap- 



