TREES AND SHRUBS 5 



A PLEA FOR THE USE OF OUR NATIVE PLANTS 



The condtions necessary for the growth of plants are (1) 

 food upon which they can subsist, both in the soil and in the 

 air; (2) moisture in proper quantity in soil and air; (3) a 

 certain total amount of heat during the growing season, as 

 well as a temperature that is neither too high nor too low; 

 and (4) a favorable amount of light. Different regions upon 

 the earth's surface differ greatly in respect to the degree in 

 which they supply these conditions, and, as a consequence, 

 different localities have native floras which resemble each 

 other in about the same degree as the growing conditions of 

 the localities themselves approximate each other. 



The degree to which the growing conditions may be ar- 

 tificially controlled varies considerably. The chemical con- 

 tent, mechanical condition or texture, and moisture content of 

 the soil in any locality may be controlled with comparative 

 ease, if small areas only are to be considered. But the humid- 

 ity of the atmosphere, the temperature limits, and the light 

 intensity of any region out of doors can be modified but a 

 very small amount. 



In an area so large as that of our State, almost all kinds 

 of soils may be found, but the best natural soils occur only in 

 the higher mountains where they have been sheltered and 

 enriched by heavy forests. Along the foothills and on the 

 mesas the soil is apt to be more or less coarse and rocky, thus 

 requiring a great deal of water to produce plant growth. Here 

 it is usually free from an excess of the salts of potassium, 

 sodium and calcium which form the dreaded "alkali." This, 

 however, is not always true, since the presence of these salts 

 is in a degree dependent upon the kind of rocks of which the 

 adjacent mountains are composed, as well as to some extent, 

 upon the general topography of the region. In the river 

 valleys where most of our towns are built, the soil is usually 

 the silt of the river and is apt to be fine grained and poorly 

 aerated, while the underlying stratum is nearly always sand. 



