The wx-844 allele contains a fully active and complete En transposable element inserted within the Wx gene. The mutability of this allele is very high and the somatic mutability is seen in the endosperm as dark staining Wx sectors in a background of non-staining wx regions;The very high coarse pattern of waxy mutability is modified into a reduced fine pattern in the presence of the I-102 element located within the A gene in the non-autonomously mutable a-m(r) 102 allele. The modifying effect of the I-102 element on En induced excision has been found to be a general phenomenon in the En-I transposable element system. The mechanism of excision inhibition involves a defective product formation, named tnpR which competitively inhibits the En encoded product responsible for excision. TnpR has no effect on the En encoded S function mediated through tnpA;A weak En element has also been isolated from the wx-m 86246X allele which was derived from the wx-844 allele. This allele contains a deletion derivative of En and is identified as the En2 element. This element has a low M action but a weak and unstable S function. It is able to produce the tnpA product although in a reduced amount. The genetic analysis followed by molecular characterization has aided in the identification of tnpA as the Suppressor function of En;Through the study of the somatic excision events in the endosperm it has been established that the En element is lost in a substantial number of cases after it is excised from the Wx gene. Further characterization of somatic excision events suggests that transposition of En during chromosome replication is the most likely cause of the loss events observed.