The shape of kernels and cracks, in a nutshell

We explore the shape of walnut shells and kernels. We analyze 1264
individual 3D X-ray CT scan reconstructions of walnuts, corresponding to
150 walnut accessions. We exploit the nondestructiveness of X-rays to
digitally segment and measure the 4 main tissues of interest for each
walnut, namely shell, kernel, packing tissue, and sealed air. From these,
we extract a total of 38 size- and shape-specific descriptors, many of
them unexplored in the current literature. We focus on several allometric
relationships of interest, from which we draw theoretical upper and lower
bounds of possible walnut and kernel sizes. We then study correlations and
variations of these morphological descriptors with qualitative data
corresponding to traits of commercial interest like ease of kernel removal
and shell strength.