Seed by which pop raised an apple (6)
I believe the answer is:
pippin
'pop raised an apple' is the definition.
'pippin' can be an answer for 'apple' (pippin is a kind of apple). I am not sure about the 'pop raised an' bit.
'seed by' is the wordplay.
'seed' becomes 'pip' (I've seen this before).
'by' becomes 'pin' (I am not sure about this - if you are sure you should believe this answer much more).
'pip'+'pin'='PIPPIN'
'which' is the link.
Can you help me to learn more?
(Other definitions for pippin that I've seen before include "Hobbit, friend of 1 across" , "Kind of eating apple" , "Variety of eating apple" , "fruit" , "excellent example" .)