Despite extensive research, we are far from a comprehensive answer to the question of how cells and organisms adopt well-defined shapes. We addressed this question in the context of symmetry breaking and stationary elongated forms in plants and fungi, by combining experimental and theoretical approaches. Our main findings are that (i) growth is correlated with the mechanical properties of cells, (ii) these mechanical properties are determined by molecular and genetic cues, and (iii) feedbacks from shape on cell behavior, through patterns of mechanical stress, are required for the maintenance of elongated forms. More generally, our work reveals physical mechanisms that are instrumental in morphogenesis.