6 AGRICULTURE ON THE PACIFIC SLOPE 



For planting seeds in the field we may use machines 

 called drill planters, which place the seeds at just the 

 right depth. The earth may be pressed down by small 

 rollers attached to the planter, or by afterward going 

 over the field with a roller. 



How does the seed get air ? When we water a plant 

 which is growing in a pot, we see air bubbling up out of 

 the soil as we pour on the water. If we pour on enough 

 water, the air all comes out of the soil. It goes slowly 

 back into the soil again as the water drains off and the 



il dries. 



The seed needs the air in the soil just as much as it 

 needs the water. To^ supply the seed with plenty of 

 air the gardener makes a loose, open soil into which air 

 can easily enter. He does this by mixing in some leaf 

 nnold and sand. Then he gets good drainage by putting 

 < * the earth in shallow boxes with holes bored in the bot- 

 v toms, or in pots with a layer of gravel below the soil. 

 If a crust forms on the top of the soil, he breaks it up 

 jr-ot ^with a hoe or rake to let in air. 



How deep should seeds be planted? Fill a glass fruit 

 jar or bottle with earth, placing seeds against the glass 

 all the way to the bottom, so that you can see which 

 germinate first. Does the result depend on how wet 

 * the soil is and on how closely it is packed ? 



How much force do seeds exert in swelling? Figure 4 

 shows one way to find out. Some dry beans are placed 

 in an agateware cup in which holes are punched to let 



