Tobacco cells transformed by the T37 strain of Agrobacterium tumefaciens will, when cloned and grown in culture, produce abnormal though recognizable shoots (teratomas). These shoots will, when grafted to healthy host plants, grow and become morphologically, histologically and functionally identical to healthy shoots. However this suppression of tumor growth is reversible for when apparently normal tissues are returned to culture they quickly resume the growth habit and characteristics of the original teratoma culture. An irreversible suppression or recovery occurs when the shoots flower. Plants grown from the seed or pollen of the teratoma shoots seem normal by all established criteria including growth habit in culture. The major objectives of the proposed research program are as follows: 1) A microscopic examination of teratoma shoots in cloned cultures will be undertaken to determine the morphological basis for abnormal growth and whether certain cell types are better able than others to resist continued neoplastic division. 2) Specialized cell types in teratoma shoots, such as leaf hairs, will be cloned to determine whether differentiation leads to recovery from the disease. 3) Meristem-tip culture of teratoma shoots will be initiated to determine whether recovery from the disease follows the pattern of plant virus elimination. Systemic plant viruses do not usually invade the apical meristem. 4) Recovered cells will be treated with halogenated pyrimidines in culture to determine whether neoplasia can be induced as it is in certain animal cell systems. This would suggest that recovery is due to the suppression of viral function. 5) An analysis of vessel member differentiation in plant cultures will be undertaken to determine whether cells arrested in the S phase of the cell cycle with fluorodeoxyuridine are able to differentiate when placed on an appropriate inductive medium.