Solid assemblies of organic compounds often include some inevitable misfit between constituents, giving rise to geometric frustration. In order to fit into the assembly the molecular building blocks must distort. In many cases, for small enough assemblies there are non-local compromises that are more energetically favourable. These are associated with non-uniform distortions and highly cooperative response between the constituents. This may result in tendency to form filaments, lattice distortions and large morphological variations during the growth of the assembly. In the proposed experiment, we will follow the morphological evolution and branching of slender protein single crystals formed by a living organism. This will not only provide the first experimental evidence to geometric frustration in protein crystals, but will also demonstrate the role of spontaneous processes in biological tissue formation. We aim to provide a toolkit for controlled branching of macromolecular crystals.