Possible Clues:

• Chemical word for a small or embryonic root
• Root in the end for a rising hero
• Part of a plant embryo that develops into a root
• Root's declaring, with last pair going berserk
• Some, on reflection, feel CID arrest a bit of a nerve
• What sounds like extreme part of a plant
• Gunners take risks protecting large part of plant
• Painter taking Spanish soldier over part of plant
• I'd get in the clear to get at the root of this
• Part of plant an extremist referred to in speech