58 The dwellers in the soil 



a fresh clean look. After some time the other soil 

 becomes very compact and is covered with a greenish 

 slimy growth. When this happens carefully turn the 

 pots upside down, knock them so as to detach the soil 

 and lift them off. The soil where the earthworms had 

 lived is full of burrows and looks almost like a sponge. 

 Fig. 24 shows what happened in an experiment lasting 

 from June to October. The other soil where there were 

 no earthworms shows no such burrows and is rather 

 more compact than when it was put in. 



Earthworms therefore do three things : — 



(1) They make burrows in the ground and so let 



in air and water. 



(2) They drag leaves into the soil and thus help 



to make the mixture of soil and leaf mould. 



(3) They keep on bringing fresh soil up to the 



surface, and they disturb the surface so 

 much that it is always clean and free 

 from the slimy growth. 

 All these things are very useful and so a gardener 

 should never want to kill worms. The great naturalist, 

 Darwin, spent a long time in studying earthworms at 

 his home in Kent and wrote a very interesting book 

 about them, called Earthworms and Vegetable Mould, 

 He shows that each year worms bring up about -^ih. of 

 an inch of soil, so that if you laid a penny on the soil 

 now and no one took it, in 50 years it might be covered 

 with an inch of soil. Pavements that were on the sur- 

 face when the Romans occupied Britain are now covered 

 with a thick layer of soil. 



But besides these there are some living things too 

 small to see, that have only been found by careful ex- 

 periments, but you can easily repeat some of these 



