Another section of the population, the fungi, was simply found, and at present we have only limited views as to their function. The older workers considered that they predominated in acid soils, while bacteria predominated in neutral soils. Present-day workers have shown that fungi, including actinomycetes, are normal inhabitants of all soils. The attempts at quantitative estimations are seriously complicated by the fact that during the manipulations a single piece of mycelium may break into fragments, each of which would count as one, while a single cluster of spores might be counted as thousands. Little progress has therefore been made on the quantitative lines which have been so fruitful with protozoa. Dr. Brierley gives, in Chapters VII. and VIII., a critical account of the work done on fungi. In addition to the organisms already considered there are others of larger size. The nematodes are almost visible to the unaided eye, most of them are free living and probably help in the disintegration of plant residues, though a few are parasitic on living plants and do much injury to clover, oats, and less frequently to onions, bulbs, and potatoes. Further, there are insects, myriapods and others, the effects of which in the soil are not fully known. Special importance attaches to the earthworms, not only because they are the largest in size and in aggregate weight of the soil population, but because of the great part they play in aerating the soil, gradually turning it over and bringing about an intimate admixture with dead plant residues, as first demonstrated by Darwin. Earthworms are the great distributors of energy material to the microscopic population. Systematic quantitative work on these larger forms is only of recent date, and Dr. Imms, in Chapter IX., discusses our present knowledge. TABLE I. SOIL POPULATION, ROTHAMSTED, 1922. (The figures for algæ and fungi are first approximations only, and have considerably less value than those for bacteria and protozoa.)