Abstract
Forest dislocations have been introduced in the easy glide region of copper crystals whose impurity content varies from 5 p.p.m. to 200 p.p.m. The importance of impurity, and of forest-primary dislocation interactions in the relative magnitudes of the short-range stress, τs, and the long-range stress, τg, has been established. Impurity enhances the ratio τgg considerably in easy glide, whereas forest-primary interactions lead to a smaller ratio of τsg which is characteristic of stage II of the stress-strain curve.