Pith

A few plants, such as walnuts, have distinctive chambered pith with numerous short cavities (see image at middle right).

The term pith is also used to refer to the pale, spongy inner layer of the rind, more properly called mesocarp or albedo, of citrus fruits (such as oranges) and other hesperidia.

[2] The pith of the sago palm, although highly toxic to animals in its raw form, is an important human food source in Melanesia and Micronesia by virtue of its starch content and its availability.

Current processes for starch extraction are generally only about 50% efficient, however, with the other half remaining in residual pith waste.

Dried pith (which is actually the center of the leaf) of certain rush plants soaked in fat or grease, held using a rushlight, was used as home lighting.