Kill off melon plant growing from within (7)

I believe the answer is:

endogen

I'm a little stuck... Click here to teach me more about this clue!

'plant growing from within' is the definition.
I can't judge whether this definition defines the answer.

'kill off melon' is the wordplay.
'kill off' becomes 'end' (I've seen this in other clues. I am not sure about the 'off' bit.).
'melon' becomes 'ogen' (I've seen this before).
'end'+'ogen'='ENDOGEN'

Can you help me to learn more?

(Other definitions for endogen that I've seen before include "plant" , "Lily" .)

I've seen this clue in The Times.

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