A generalised explanation of the zoning appears to be as follows:—
In the outermost zone the actively growing mycelium decomposes soil constituents and liberates nitrogenous material which is in turn taken up by the plant roots nearby and utilised for their growth. In the penultimate zone the grass is dead, probably not caused by a direct parasitic attack but by the mycelial threads filling the air-spaces in the soil and so inhibiting water flow. This destruction of the delicate balance of water and air found in any soil induces drying out and gradual death of the plants whose roots permeate the soil. Behind the dead-zone is vegetation which shows increased vigour apparently due to plant-nutrients being released by the decaying mycelium and plant-material, whose death has been caused by the presence of the fungus. The innermost zone is not so stimulated.
With nothing more than graph and tracing paper, a tape-measure, note-book and pencil, pieces of cane about four inches long, and coloured dye or indian ink, it is exciting to assess the annual radial growth of fairy-rings and to correlate these with environmental conditions. This can be carried out on a school lawn or on a home lawn; the method and further experiments are given in [Appendix iii].
Plate 36. Fairy-ring fungus—Marasmius oreades
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Marasmius oreades (Fries) Fries Fairy-ring champignon
Cap: width 25-60 mm. Stem: width 5-9 mm; length 30-80 mm.
Description:
Cap: pinkish tan with slight flush of brown at centre, hygrophanous and drying out buff-coloured or clay-coloured, convex at first then expanding to become plane, but for an obtuse umbo which is retained at the centre.