The most common and most likely answer to this crossword clue is the 6 letter word ADNATE
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The straight part
We know that "organically grafted" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case organically grafted = adnate.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does ADNATE mean?
ADNATE adjective- Linked or fused to a structure of a type different from itself; for example, attachment of a stamen to a petal is adnate, while attachment of a stamen to another stamen is connate.
- Growing with one side adherent to a stem; applied to the lateral zooids of corals and other compound animals. in fish, having the eyes fused and unable to rotate independently