Seed covering (4)
'seed covering' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for aril that I've seen before include "appendage" , "Part of seed" , "Hairy or fleshy seed covering (botany), lair (anag.)" , "Seed cover; lair (anag.)" .)
(Other definitions for earth that I've seen before include "underground shelter" , "electrical safety precaution" , "Mud" , "cost of which is very high" , "Soil; fox's lair" .)