422 SOILS: PROPERTIES AND MANAGEMENT 



in permanent pastures and meadows are of much value 

 in this way. 



343. Worms. The common earthworm is the most 

 conspicuous example of the benefit that may accrue from 

 this form of life. Darwin, as the result of careful measure- 

 ments, states that the quantity of soil passed through 

 these creatures may, in a favorable soil in a humid climate, 

 amount to ten tons of dry earth per acre annually. The 

 earthworm obtains its nourishment from the organic 

 matter of the soil, but takes into its alimentary canal the 

 inorganic matter as well, expelling the latter in the form 

 of casts after it has passed entirely through the body. 

 The ejected material is to some extent disintegrated, and 

 is in a flocculated condition. The holes left in the soil 

 serve to increase aeration and drainage, and the move- 

 ments of the worms bring about a notable transportation 

 of lower soil to the surface, which aids still more in effect- 

 ing aeration. Darwin's studies led him to state that from 

 one-tenth to two-tenths of an inch of soil is yearly brought 

 to the surface of land in which earthworms exist in normal 

 numbers. 



Instances are on record of land flooded for a consider- 

 able period so that the worms were destroyed, and the 

 productiveness of the soil was seriously impaired until it 

 was restocked with earthworms. 



Wollny conducted experiments with soil, the soil in one 

 case containing earthworms and in another case not con- 

 taining them. Although there was much variation in his 

 results, they were in every case in favor of the soil con- 

 taining the worms, and in a number of the tests the yield 

 on rich soil was several times as great as where no worms 

 were present. 



Earthworms naturally seek a heavy, compact soil, and 



