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