Sentence:  The <WSD>specific</WSD> staining by both direct and indirect methods showed that WTV antigen was concentrated in the pseudophloem tissue and in a few thick walled cells in the xylem region , but was not detectable in any other tissues of the root and stem tumors . 
Meaning of the word marked with <WSD> tags:  (sometimes followed by `to') applying to or characterized by or distinguishing something particular or special or unique