Cereal plant discovered, seedy inside (6)
I believe the answer is:
millet
'cereal plant' is the definition.
(millet is a type of cereal plant)
'discovered seedy inside' is the wordplay.
'discovered' becomes 'met' (discover can mean to meet or encounter).
'seedy' becomes 'ill' (seedy can mean unwell).
'inside' is an insertion indicator.
'met' going around 'ill' is 'MILLET'.
(Other definitions for millet that I've seen before include "Type of cereal" , "Cereal plant producing large crop of small seeds" , "Cereal plant or 19th century French painter" , "Seed from cereal grasses - French painter, d.1875" , "Cereal - French painter, d. 1875" .)