The spongy tissue in the rind of oranges (4)
I believe the answer is:
pith
(Other definitions for pith that I've seen before include "hats may be made of this" , "Spongy tissue like that lining an orange skin" , "White tissue under the rind of citrus fruit" , "Tissue inside the rind of citrus fruits" , "Essence; tissue inside rind" .)