

SOIL MICRO-ORGANISMS 389 



258. 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 care- 

 ful measurements, states that the amount 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 movements of the worms bring about a notable 

 transportation of lower soil to the surface, which aids 

 still more in effecting aeration. Darwin's studies 

 led him to state that from one-tenth to two-tenths 

 of an inch of soil is brought to the surface of land in 

 which earthworms exist in normal numbers. 



Instances are on record of land flooded for a con- 

 siderable period so that the worms were destroyed, 

 and the productiveness of the soil was seriously 

 impaired until it was restocked with earth-worms. 



Wollny conducted experiments with soil, in one 

 case containing earthworms, and in another destitute 

 of them. Although there was much variation in his 

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

 containing 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. 



