The Formation of Constricting Rings in Nematode-catching Hyphomycetes Grown in Pure Culture

SUMMARY Constricting rings are normally formed in the presence of nematodes. The fungi can be induced to form rings if treated with certain organic substances such as animal extracts and sera. One of the fungi discussed, Arthrobotrys dactyloides Drechsler, will produce rings without the addition of stimulants. Ring formation is not due to starvation of the fungus. An experiment describing the growth of the fungi on to cover-glasses indicates that the rings may be initiated as a result of the contact with the glass surface.