COLORADO WILD FLOWERS 



13 



As is well known, plants reach greatest luxuriance in the tropics 

 where, in addition to high temperature, there are to be found wet soil 

 and damp atmosphere. On mountain summits of the Rockies the 

 opposite conditions prevail. The air temperature is low every night 

 in the year. Rainfall is not great. The soil is never warmed except 

 for a few inches at the top. This cold soil makes the roots sluggish 



Fig. 13. — Rock Ridge Country of Northern Colorado 

 In this part of the foothill region the valleys have a dense covering of long grass 

 while the ridges support shrubs of mountain mahogany and scattered pines. 



in their work and they cannot absorb, much moisture. Hence, even 

 though there be plenty of moisture in the ground the soil may be con- 

 sidered '"dry" with reference to plants. They cannot make use of the 

 water which is present in the, soil. 



In addition to the inability of roots to absorb moisture there must 

 be considered the high winds which rapidly dry out vegetation and the 



