Sentence:  In the direct method , * * f , not <WSD>further</WSD> treated , stained certain tissues of healthy sweet clover stems nonspecifically and WTV tumor sections were similarly stained by comparable * * f . 
Meaning of the word marked with <WSD> tags:  to or at a greater extent or degree or a more advanced stage (`further' is used more often than `farther' in this abstract sense)