Sentence:  Of the numerous substances tried, the one which seems best to fulfill these conditions is powdered <WSD>hellebore</WSD>. Some of the powdered <WSD>hellebore</WSD> in use is prepared from the roots of a plant which botanists know as "Veratrum viride", and which is popularly known as Indian polk or itch weed. 
Meaning of the word marked with <WSD> tags:  A toxic extract of certain false hellebores ((noshow=1) or (noshow=1)), formerly used as a pesticide.