Crossword Genius

Petri dish filler (4)

Ross

I believe the answer is:

agar

'petri dish filler' is the definition.
(I've seen this in another clue)

This is the entire clue.

(Other definitions for agar that I've seen before include "setter" , "Substance derived from seaweed" , "Seaweed jelly" , "Jelly medium" , "Seaweed derivative" .)

I've seen this clue in the LA Times and The New York Times.
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