In exercise barrel in auditorium starts to show flower (7)
I believe the answer is:
petunia
'flower' is the definition.
(petunia is a kind of flower)
'in exercise barrel in auditorium starts to' is the wordplay.
'in exercise' becomes 'pe' (Physical Education. I am not sure about the 'in' bit.).
'barrel' becomes 'tun' (tun is a kind of barrel).
'starts to' says to take the initial letters.
The initial letters of 'in auditorium' is 'ia'.
'pe'+'tun'+'ia'='PETUNIA'
'show' acts as a link.
Can you help me to learn more?
(Other definitions for petunia that I've seen before include "Flowering plant" , "Popular plant for baskets" , "Flower much used in hanging baskets" , "Plant cultivated for its white, pink, blue or purple funnel-shaped flowers" , "Garden plant, originally from S. America" .)