For instance, at the cellular scale, cell types are viewed as balls rolling down a hilly landscape, where valleys are differentiation trajectories, from stem cells at the top to lower specialized cells at the bottom. These simple diagrams allow researchers to depict and share diverse phenomena, such as cell-cell communication (Fig. ). Each layer may be built by integrating experimental data from various sources, such as gene sequences, cell's gene expression profiles or tissues' spatial omics (Fig. ). Since tissues are made of cells, themselves composed of biomolecules, we suggest that this formalism may allow a "vertical" flow of information across scales (Fig. ). Similarly, "horizontal" information transfer may be envisioned within a layer (Fig. ). The purpose is to offer a simple mental image of complex organs and eventually generalize their principles to new material-producing organoids. As diagrams may be abstract, Figure provides a more detailed representation of hierarchical landscapes. At the tissular scale, valleys represent the multiple developmental routes discussed in the previous section (Fig. ). The width of a valley, or canalization, indicates how robust development is to perturbations. For example, the "Picasso frog" can self-correct significant embryonic defects 414 . Each location represents an organ state, composed of multiple cell types structured together and linking this tissular scale to the next.