Sentence:  With fresh material, taxonomic conclusions are leavened by recognition that the material examined reflects the site it occupied; a herbarium <WSD>packet</WSD> gives one only a small fraction of the data desirable for sound conclusions. Herbarium material does not, indeed, allow one to extrapolate safely: what you see is what you getnb.... 
Meaning of the word marked with <WSD> tags:  A specimen envelope containing small, dried plants or containing parts of plants when attached to a larger sheet.