IMPROVEMENT OF SOILS. 93 



plant is killed during growth in any one lot, a plant 

 must be removed in the other lot to keep the balance 

 even. Be particularly careful to note all the facts of 

 the work ; because there may be some apparently tri- 

 fling circumstance, such as the neighborhood of a 

 manure-heap, that may quite upset all calculations, and 

 render the results quite misleading. 



It is not difficult to see why tillage improves the 

 plants growing in any soil. After every rain the sur- 

 face of the soil appears to be hard, as if a crust had 

 formed on top. In sandy soils this is slight, but still 

 it is to be seen ; and on clay soils it is often quite 

 thick and hard. Every drop that falls seems to beat 

 the soil down ; and when the sun and winds dry up 

 the soil, after the rain has passed, the top of the earth 

 is like the top of a well-baked loaf. Through this 

 crust very little air can pass, and the roots of the plants 

 are sealed up as if in a close box. With a rake we 

 easily break up this crust, and open the soil to the air. 

 The oxygen of the air can then enter the soil through 

 millions of minute holes and passage-ways, combining 

 with elements brought down by the rain or already 

 existing in the soil ; and the plant, finding fresh food 

 prepared for it, greedily stretches out its roots to get 

 it. No doubt the fresh air thus allowed to penetrate 

 the soil also ventilates and purifies it, and makes it a 

 sweeter and more healthful home for the plants. The 

 loose, broken surface, left after the crust formed by 

 rain has been removed, also offers millions of fine 

 points on which the dew may condense, and thus more 



