Plant material (9)
I believe the answer is:
cellulose
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">plant material</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for cellulose that I've seen before include "film-makers use it" , "Polysaccharide" , "Plant material" , "Main constituent of plant cell walls" , "O cull eels for what causes the pitted look" .)