68 AGRICULTURE ON THE PACIFIC SLOPE 



FIG. 38. Several kinds of harrows: (1) disk, (2) spike tooth, (3) Acme, 

 (4) spring tooth with side frames. 



Rollers. When either of the tools described have left 

 the ground too loose and open, especially after seeding, 

 heavy rollers made of wood or iron are sometimes used to 

 compact the surface a little, and press the moist ground 

 around the seeds so that they may sprout better. Rollers 

 are also used to break clods on tilled ground, and for that 

 purpose are channeled, or made of square iron bars. 



Earthworms. We should not forget that earthworms 

 till the soil continually, except when the weather is 

 too cold for them to work. They are constantly mov- 

 ing about in the soil, and help to keep it loose and open 



