In ultrathin sections of tumorous tissues of white clover plants artificially infected by grafting with the clover enation virus nuclei and nucleoli were very much enlarged. Such nuclei contained massive amounts of tubular particles in crystalline array. In spaces between the nuclear membrane lamellae such particles had an additional coat and usually occurred in irregular accumulations. These bacilliform particles measured about 200 • 80 m~z. This virus was not found in normal tissues.Two other viruses with elongated particles of 475 and 665 m~ were also observed in non-neoplastic tissues. They were easily detected in negatively stained chop preparations, rapidly transmitted by sap, and considered to be mere contaminants.Enation virus diseases are heterogeneous in epidemiology and etiology. Several have recently been found associated with dense accumulations of big spherical or polyhedral virus particles. The virus detected here closely resembles several bacilliform viruses described in recent years. These viruses are quite different in symptomatology and epidemiology.