Several species of mushrooms growing in circles in lawns and golf greens cause a condition known as fairy ring, rather common when the soil is quite moist and contains a superabundance of organic matter. Less commonly, some of these mushrooms are responsible for a poor condition of other herbaceous plants and of roses. The chief symptom in turf is the appearance of continuous or interrupted bands of darker green, due to the fungus mycelium breaking down organic matter into products easily assimilated by grass roots. Following the zone of stimulated growth there may be a zone of dying grass due to temporary exhaustion of nutrients, or to toxic substances from the mushroom mycelium, or because a layer has developed that is rather impervious to water. The green rings are more conspicuous on underfertilized lawns, and their presence can sometimes be masked by adequate fertilization. Breaking off the mushrooms, possibly spiking the sod, is all the control ordinarily recommended.