SOIL AND SUBSOIL. 159 



habit of drawing after themselves into their burrows leafstalks, 

 blades of grass and other vegetable remains, renders their work 

 of no mean importance both from the physical and chemical 

 point of view. The uniformity, lack of structure and loose 

 texture of the surface soil, especially of forests, as compared 

 with subsoil layers of corresponding thickness, is doubtless 

 largely due to the earthworms' work. It has frequently been 

 observed that when an unusual overflow has drowned out the 

 earthworm population of a considerable area, the surface soil 

 layer remains compacted, and vegetation languishes, until new- 

 immigration has restocked the soil with them. Again, the 

 humus formed under their influence is always neutral, never 

 acid. 



Wollny (Forsch, Agr., 1890, p. 382), has shown by direct experimental 

 cultures in boxes, with and without earthworms, surprising differences 

 between the cultural results obtained, and this has been fully confirmed 

 by the subsequent researches of Djemil (Ber. Physiol. Lab. Vers. 

 Halle, 1898). In Wollny's experiments, the ratio of higher production 

 in the presence of the worms, varied all the way from 2.6 per cent in 

 the case of oats, 93.9 in that of rye, 135.9 m that ^ potatoes, 300 in 

 that of the field pea, and 140 in that of the vetch, to 733 per cent in 

 the case of rape. Wollny attributes these favorable effects in the main 

 to the increased looseness, and perviousness of the soil to air, and 

 diminished water-holding power. DjemiPs results all point in the same 

 direction ; and he shows, moreover, that the allegation that the roots 

 penetrate more deeply in the presence of the worms by following their 

 burrows, is unfounded, the descending roots often passing close to and 

 outside of these. 



The work of earthworms is especially effective in loamy soils 

 and in the humid regions. In the arid region, and in sandy 

 soils generally, the life-conditions are unfavorable to the 

 worm, and the perviousness elsewhere brought about by its 

 labors already exists naturally in most cases. It is stated by 

 E. T. Seton (Century Mag. for June, 1904) that the earth- 

 worm is practically non-existent in the arid region between the 

 Rocky Mountains and the immediate Pacific coast, from Mani- 

 toba to Texas. In the Pacific coast region, however, they are 

 abundant, and do their work effectually. 



