Seed-corn? (5)
I believe the answer is:
grain
This clue is a double definition.
'seed' is the first definition.
(grain is a kind of seed)
'corn?' is the second definition.
(corn is a kind of grain)
(Other definitions for grain that I've seen before include "Single piece of sand etc" , "Cereal as food" , "Small hard seed of corn etc" , "Tiny amount" , "Smallest measure of weight in avoirdupois" .)