Plants of Pisum sativum var. arvense Poir. cv. Dun were grown with two equal shoots kept in different light conditions. In these plants a darkened shoot was inhibited and it eventually withered and died; it elongated and became etiolated only when the shoot in the stronger light was removed. A similar result was obtained in simulated ecological conditions, when the shoot in the inferior light was merely shaded: this shoot was severely inhibited, though it did survive. The inhibition of the shaded shoot was more pronounced when the plants were stressed by the removal of large parts of their cotyledonary reserves. These results demonstrate an integration of responses to the light environment with the correlative inhibition between shoots of the same plant. This integration enables the plant to use its developmental resources optimally in heterogeneous environments, rather than merely growing where conditions are ‘appropriate’.