PLANT COMMUNITIES OF SANDY SOIL 327 



Aster armeriaefolius ; seen only in rather loose sand. 



*Chrysopsis viscida; abundant in all soils. 



*Chrysothamnus linifolius; frequent in pure sand which is but slightly compacted. 



Coleoxanthus umheUatus; infrequent in rather fine grained sand among rocks. 



Gaillardia arislata; in coarse sand and disintegrated granite. 



Machaeranthera aspera; infrequent, in all soils. 



Senecio fendleri; a plant common in primitive growths of foothill and montane 



zones, present here in coarse soil. 

 Senecio pudicus; rare, in compact sandy soil. 



Senecio sparlioides; in the various soils, especially where there is some humus. 

 Solidago glaberrima; in moister situations, sandy soil with some humus. 



V. SUMMARY 



The article presents an account of the vegetation of a sandy 

 area in Clear Creek Canyon near Georgetown, Colorado, in the 

 Rocky Mountains, at an altitude of 8500 feet. Physiography 

 and climate are first briefly considered and then the plant com- 

 munities of each habitat are described. Chief attention is paid 

 to a shrub association, developing typically in loose sand, the most 

 characteristic species of which are Symphoricarpos vaccinoides, 

 Rhus trilobata, Ribes inebrians, and Chrysothamnus linifolius. 

 Other plant communities represented on pure sand are the wheat- 

 grass association and the short-grass association. Wheat grass, 

 Agropyron smithii, is an effective sand binder. Brief mention 

 is made of the coarser soils having only a moderate amount of 

 sand and the associations developing thereon. There is some 

 discussion of the genetic relationships of the different communi- 

 ties. It is pointed out that the shrub communities are to be 

 considered as intermediate ecologically between grassland and 

 coniferous forest, that well-compacted soil tends to forest on 

 steeper slopes and to grassland on level ground. A map of the 

 area studied and two photographs are used for illustration. An 

 annotated list is given of 64 species of seed plants occurring in 

 sandy soil with a special designation of those which are most 

 important. 



