1. Further evidence indicating a physiological change in cell activity resulting from breaks and rearrangements of chromosome parts has been obtained from the paired mosaics in the endosperm. In the majority of cases of paired losses of C and Rr, g and Su, Pr and Su, no change in size, arrangement or numbers of cells is apparent. In a few cases marked changes in some or all of these respects are noted. In the same material one part of the paired mosaic area may be affected, in other cases the other part is affected. This means that many chromosomal rearrangements are withaut any effect upon cell activity other than the subtraction of the usual action associated with the dominant allele. In the few cases where profound physiological alterations occur it seems apparent that specific places of breakage and reattachment are involved. If the alteration resulted from a shift of growth-controlling regions of the chromosomes or a general unbalance in amount or kind of chromatin material, paired alterations showing the changes in growth would be expected more frequently and both parts of the paired mosaic areas would be affected. A few cases of this latter type are noted but they are not general.