THE SOIL. 25 



weather will permit, so that none may be wasted by 

 evaporation, or used up by wjeeds before the 

 desired crop begins to grow. Early planting is 

 generally best, for the roots of plants not only 

 drink in their full share of water early in the sea- 

 son, but the ground is soon shaded by the growing 

 leaves crowding out the weeds, which would claim a 

 part of the soil nourishment. They also prevent 

 early winds from drying the soil by not allowing 

 them such free access to the surface, from which 

 they take away the moisture very rapidly. All 

 have noticed the drying effect of wind, even when 

 the sun is not shining. It often does its work as 

 rapidly during the night as during the day. A 

 hedge-row, a fence, or even a strip of ground with 

 a higher growth of plants, will so break the force 

 of wind that little loss will result. Winds are 

 beneficial in many ways, but a very mild one may 

 do a vast amount of damage. 



SOIL AIR. 



Surrounding the entire earth is a layer of air 

 many miles high. It is invisible and very light; yet, 

 on account of its great volume, gravity exerts 

 such a pull on it that it presses heavily, about four- 

 teen pounds to the square-inch, everywhere upon 

 the surface of the earth. It presses heaviest, of 

 course, upon the lowest places. Air, which is so 

 essential to plant and animal life, and to the for- 

 mation of mineral compounds, is composed mainly 



