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UNIVERSITY OF COLORADO STUDIES 



Mountain Mahogany. Cercocarpus parvifolius Nutt. — One speci- 

 men of this shrub is found on Long Mesa, on the south crest toward the 

 top. On Horse Mesa, however, it forms an extensive society on the 

 north crest extending on to the top and down on the north slope. Exactly 

 similar habitats may be found on Long Mesa and it is only a matter of 

 chance distribution that it is not found there. 



Fig. io. — Sumac. Rhus glabra L. — Sumac reaches its maximum development on 

 the south exposure at the upper part of the mesa. Here it dominates large areas, occurring 

 in stony soil. Masses of the shrub are found in the open places among the pines on the 

 upper part of the mesa top. In Pole Canyon it occurs just outside the Crataegus zone 

 in drier soil. None occurs in Cemetery Gulch. Sumac seems able to grow in habitats 

 having very different physical factors. Its discontinuous distribution is probably due to 

 competition rather than to differences in the physical conditions. 



Roses. RosasayiSchwe'm.; R. fendleri Crepin; R. nutkana Presl.; 

 R. pratincola Greene. — The roses form a layer underneath the Crataegus. 



