THE ROOT 227 



(a) The Soil, and hoiu Water exists in the soil. — When a well 

 is dug or the foundation of a house is laid, we can see that the 

 soil has di^fferent layers. The topmost layer is mostly a thin- 

 grained layer of earth, more or less black, containing humus, 

 i. e., decayed organic matter. Then follows the sub-soil with less 

 humus and larger pebbles or pieces of rock, and beneath that 

 there is solid rock; it mav be laterite, as on the West Coast of 

 India; or Granite and Gneiss, as in the Ghats; or vulcanic rocks, 

 as in the Deccan ; or any other of the various kinds of rock. By 

 the mechanical action of water and wind; the changes of temper- 

 ature; the chemical action of air and water; and the action of 

 plant-roots and burrowing animals the rock, where it lies bare 

 and open, is broken up and weathered, and soil is produced. 



The parts of w^iich surface soil exists can be found by the 

 following experiment. Put some garden soil into a small basin 

 with water, and stir it well. The lighter substances now come 

 to the surface of the water: they are chiefly vegetable mould and 

 other decayed organic matter (humus). Take the humus off. 

 Now pour the remaining muddy water into another basin leaving 

 the heavy and hard particles in the first basin, and allow the 

 water in the second basin to evaporate: a crust of clay remains. 

 Wash the remainder in the first basin again and again: the hard 

 particles will be found to consist mainly of sand. The main 

 parts then of which the surface soil consists are vegetable mould, 

 clay and sand. 



Now, how does water exist in the soil? Take three flower-pots. 

 Fill the first with pure sand, the second with pure clay, and the 

 third with good garden soil. Pour water in each of the pots. 

 Which of the three retains most w^ater? The pot with clay does 

 not allow the water to percolate; the one filled with sand absorbs 

 the water quickly and after a short time the water trickles through 

 and runs out from the hole at the bottom of the pot. But in the 

 third pot, containing a mixture of sand, clay and humus, water 

 soaks well and is retained best. According to the proportion of 

 sand and clay mixed in garden soil, the degree of its power of 

 retaining water varies. 



Of great importance to the fertility of the soil is the question, 



15* 



