118 H^XPERIMENTS WITH PLANTS 



soil, i. e., soil in which the spaces are filled with 

 water instead of air I This level is called the water- 

 table; does the height of water in a well indicate this 

 point reliably ? From how great a depth is the water 

 drawn up by the soil ? Get a glass tube about six 

 feet long, or make one by joining together short 

 lengths by means of rubber tubing. Fill this with 

 clay (dried and pulverized), and place the lower end 

 in water; it may be several weeks before the water 

 stops rising. Clay lifts further than sand, because the 

 spaces between the particles are smaller, but it cannot 

 apparently lift more than six feet.^ This means that 

 practically all water which sinks five or six feet below 

 the roots of a plant is permanently lost to that plant. 

 Moist soil draws up water more rapidly than dry, but 

 can lift it no higher. 



Find out what you can about the height of the 

 water-table in your vicinity at various seasons of the 

 year; does it follow exactly the elevations and depres- 

 sions of the surface of the land ? How many feet does 

 it rise and fall yearly ? What is the ideal depth for the 

 water-table? Does the rise of the water-table in 

 spring help to thaw out the ground ? 



From these experiments it appears that in soil 

 which is moist and in good condition for growing 

 plants (but not wet) the water exists in the form of 



iThe finest silt may lift water as high as ten feet: this necessarily 

 occupies a very long time. 



