26 



AGRICULTURE 



of air. Some air reaches the roots of plants in water, but it is 

 excluded from close, saturated soils. 



You may have seen stunted, sickly-looking stalks of corn in a 

 marshy place, while near by on better-drained land were large, 

 thrifty plants. In wet land, the roots' supply of air is so limited 

 that growth is stunted. Certain plants, such as rice, are adapted 

 to saturated soils, as fish are to water. But most agricultural 

 plants need well-drained soil. There are millions of acres of land 

 in the United States which need drainage to make them productive. 



EXPERIMENTS 



i.. Fill a glass with gravel or small pebbles and pour into it as much 

 water as is needed to wet them, that is, to form water films around each 

 one without leaving any free, or standing, water. Crush the pebbles as 



fine as you can so as to form a 

 coarse sand, and see how much 

 water is required to wet this. 

 Which requires more water, the 

 pebbles or the sand, and why? 

 2. Put a layer of gravel in a 

 pan and then fill it with water. 

 Put in this three glass tubes 

 of different sizes, supported in a 

 rack or frame. Notice that the 

 smaller the tube is, the higher 

 the water rises. Thus water 

 rises higher through small soil 



ILLUSTRATION OF EXPERIMENT 2 



and 4 described on page 21. 



spaces than through large ones. 

 3. Repeat experiments 3 

 What force causes water to descend 



in the soil ? What force causes it to rise ? 



4. Put a plant with long roots in a bottle nearly full of water. Put 

 paper around the stem and cover it with paraffin so as to make the bottle 

 air-tight. Measure the height of the water and weigh the whole. Meas- 



