Sentence:  The specific 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 <WSD>xylem</WSD> region , but was not detectable in any other tissues of the root and stem tumors . 
Meaning of the word marked with <WSD> tags:  the woody part of plants: the supporting and water-conducting tissue, consisting primarily of tracheids and vessels