390 THE PRINCIPLES OF SOIL MANAGEMENT 



Earthworms naturally seek a heavy, compact soil, 

 and it is in soil of this character that they are most 

 needed, on account of the stirring and aeration they 

 effect. Sandy soil and the soils of the arid regions, 

 in which are found few or no earthworms, are not 

 usually in need of their activities. 



259. Insects. There is a less definite, and probably 

 less effective, action of a similar kind produced by 

 insects. Ants, beetles, and the myriads of other bur- 

 rowing insects and their larva? effect a considerable 

 movement of soil particles, with a consequent aeration 

 of the soil. At the same time they incorporate in the 

 soil a considerable amount of organic matter. 



260. Large fungi. The larger fungi are chiefly con- 

 cerned in bringing about the first stages in the decom- 

 position of woody matter, which is disintegrated 

 through the growth in its tissues of the root-mycelia 

 of the fungi. These break down the structure, and 

 thus greatly facilitate the work of the decay bacteria. 

 Action of this kind is largely confined to the forest 

 and is not of much importance in cultivated soil. 



Another function of the large fungi is exercised 

 in the intimate and possibly symbiotic relation of the 

 fungal hyphae to the roots of many forest trees, in 

 soil where nitrification proceeds very slowly, if at all, 

 for nitrates are apparently never present in forest 

 soils. This enveloping system of hyphse, which may 

 consist of masses in a definite zone of the cortex, 

 with occasional filaments passing outward into the 

 soil, or which may surround the root with a dense 

 mass of interwoven hyphse, is called mycorhiza. 



