SOILS 13 



particles has more surface exposed than soil with coarser 

 particles is illustrated by an apple. The surface of a whole 

 apple is represented by the peeling. If the apple is quartered, 

 or cut into many pieces, each cut increases the exposed 

 surface of the apple by the two newly cut surfaces. The 

 apple is no larger. The exposed surface represented by 

 the peeling is the same. If a grain of sand is pulverized 

 to form many particles of clay, the amount of surface will 

 be greatly increased. Because clay holds moisture better, 

 it warms up more slowly in the spring. Crops start more 

 slowly, but are much less Ukely to be injured by drouth. 



Questions: 



1. What do you understand by the terms, gravel, sand, clay? 



2. Tell the difference between a sandy loam, and a clay loam. 



3. Explain why clay soil holds moisture better than sandy soil. 



Arithmetic : 



1. If a cubic foot of sandy soil weighs 90 lbs. and holds 17% of 

 its weight of water, how many pounds of water will it hold? 



2. If a cubic foot of clay soil weighs 75 lbs. and holds 30% of 

 its weight of water, how many pounds of water will it hold? 



SOURCES OP PLANT FOOD 



Plant Food in the Air. — Plants as well as animals must 

 have food; and it is as important to know what plants 

 need and how to supply their needs as it is to know how to 

 feed animals properly. 



The greater portion of the plant food comes from the 

 air rather than from the soil. All those substances in a 

 plant called carbohydrates as starch, sugar and fibrous 

 tissue, are made entirely from carbon dioxide gas and 

 water. The plant takes in carbon dioxide from the air, 

 through its leaves, and water from the soil, through its 

 roots. When the water and the carbon dioxide are brought 

 together in the leaves of the plant, and the sun shines on 

 the leaves, the sun and the green coloring matter (the 

 chlorophyll) in the leaves cause the water and the carbon 

 dioxide to unite. The oxygen and hydrogen in the water 

 unite with the carbon in the carbon dioxide. These three 

 elements form starch. The oxygen in the carbon dioxide 

 is liberated and given off to the air. In this way plants 

 purify the air for animals to breathe and animals exhale 

 air containing carbon dioxide, which furnishes food for 



