PHYSICAL PROPERTIES OF sblLS. 43 



Rain water is the great carrier, the distributor, and, 

 to some extent, the manufacturer, of plant food, and 

 unless there is a free passage for it through the soil, 

 the food of plants will not be well prepared, nor will 

 the stationary plant root be properly fed." 



Relations of 8oil to Water. — All soils have 

 the power of absorbing and retaining water, but the 

 extent to which this can be done differs much, depend- 

 ing on the composition of the soil and its porosity. 

 A soil with large pores, as coarse sand, allows water 

 to percolate or run through it readily, retaining little. 

 Water poured on a soil with many small pores will 

 permeate it, saturating it thoroughly, and the soil will 

 hold much of it, unless the pores are very small, in 

 which case the water may not be able to enter them. 



Soils not only have the power to hold some of the 

 water which passes through them but also the power 

 of drawing water from below and holding it. This 

 is known as capillary power. The action of the soil 

 in this respect is like that of a lamp-wick in drawing 

 up oil. If the bottom of a tube containing soil is 

 placed in contact with water, the latter will be drawn 

 up one, two, three or even more feet owing to the 

 character and fineness of division of the soil. The 

 soil will take up so much in this way that if a little 

 more water is poured into the top of the tube, the 

 water will begin to run out below. Good soils will 

 frequently absorb and hold one-half or more of their 

 own weight of water; some will hold much more than 

 this. Those with a large pecentage of humus will 

 hold the largest percentage of water. 



Soils also have the power of absorbing moisture or 

 vapor of water from the air. This is called hygro- 



