The blue arrow in the upper right corner of the photo points to a well developed shell. Now that the shell is fully formed, the nut can no longer increase in size.
The red arrow points to the outer skin or seed coat of the developing kernel. Just inside seed coat (yellow arrow) you can see a light-green gelatinous zone. This is the very start of kernel deposition. Kernel tissue grows from the seed coat inward, eventually filling the seed cavity. Once the cavity is filled, kernel deposition continues, compressing the packing material (green arrow) between the kernel halves and against the inside of the shell.
If a pecan tree runs out of water during the kernel filling period, kernel deposition will be inhibited. At harvest, drought stricken trees will produce nuts with small kernels that have a hollow crease in the center of each kernel half, both symptoms of inadequate nut filling.
