Steiner draws attention to the many different kinds of nematodes which play a part in the biology of the soil and considers them especially as parasites of plant roots. He points out the benefits accruing from soil sterilization by steam and chemical fumigants and attributes these largely to the destruction of harmful nematodes. He devotes particular attention to the root-knot nematode, Heterodera marioni, discussing many aspects of its biology and its host-parasite relationships, including resistant hosts such as Crotalaria spectabilis and Solarium grandiflorum, in both of which the seedlings may be injured but not the adult plants. Some pages are given to accounts of sedentary nematode parasites including certain cyst-forming species of Heterodera, amongst which he describes and gives photographs of H. weissi n.sp., which occurs on the roots of Polygonum pennsylvanicum and other Polygonum spp. in the U.S.A., east of the Rocky Mountains. He reports Rotylenchulus reniformis from the roots of Jacquemontia tamnifolia and Cassia tora, grown in the U.S.A. Another section of the paper is given to accounts of migratory nematodes amongst which the following new forms are figured and described, generally in short footnotes: Criconemoides citri n.sp., from the roots of sour orange; Criconema civellae n.sp., from roots of Citrus grandis[Citrus maxima]; Paratylenchus elachistus n.sp., from roots of ramie (Boehmeria nivea); Pratylenchus leiocephalus n.sp., from roots of peanut (Arachis kypogaea) and maize (Zea mays). In addition, Dolichodorus heterocephalus Cobb, 1914, known hitherto only from freshwater sites in the U.S.A., is reported from celery roots, and an entirely new form, Belonolaimus gracilis n.g., n.sp., is figured and briefly diagnosed; morphologically it is somewhat related to Dolichodorus and was found in roots of slash and long-leaf pine and maize roots.