Sentence:  With fresh <WSD>material</WSD>, taxonomic conclusions are leavened by recognition that the <WSD>material</WSD> examined reflects the site it occupied; a herbarium packet gives one only a small fraction of the data desirable for sound conclusions. Herbarium <WSD>material</WSD> does not, indeed, allow one to extrapolate safely: what you see is what you get... 
Meaning of the word marked with <WSD> tags:  (sample or specimens for study)A sample or specimens for study.