66 COMPANION TO TROPICAL READERS 



Expt. 121. Removal of Water by Artificial Drain- 

 age. 



(a) Observe how the shallow gutters at the side of 

 the road carry off the excess of water that falls during 

 a heavy rain. 



(b) Examine deep drainage trenches in cultivated 

 land, especially near the sea. Water may often be 

 noticed running continually in them, even in dry 

 weather. 



Expt. 122. Lime as an Aid to Free Drainage. 



(a) Bore some holes in a pan and nearly fill it with 

 powdered clay; pour water in, and notice how slowly it 

 drains through. 



(b) At the same time get another pan and put in it a 

 mixture of powdered clay and " white lime ". It will be 

 observed that in this case the water drains through much 

 more freely. 



HOW WE ROB THE SOIL 



(See Tropical Readers, Book II, pp. 95-98.) 



Expt. 123. Under Natural Conditions Plants return 

 Matter taken from the Soil. Collect and examine some 

 of the surface soil in an uncultivated woodland, and ob- 

 serve that it is dark in colour and composed of decayed 

 leaves and vegetable matter. On the ground will be 

 found leaves from the trees above in various stages of 

 decomposition. 



Expt. 124. Soils become Exhausted when Con- 

 tinually Cropped. In the School Garden grow plants 

 repeatedly on one plot without adding manure; observe 

 that after a time the plants grown there become weakly 

 and yield poor crops. 



Expt. 125. One Reason for practising Rotation of 

 Crops. Examine the root system of a turnip and of 



