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 xylem <WSD>region</WSD> , but was not detectable in any other tissues of the root and stem tumors . 
Meaning of the word marked with <WSD> tags:  a part of an animal that has a special function or is supplied by a given artery or nerve