Sentence:  The specific staining by both direct and indirect methods showed that WTV antigen was concentrated in the pseudophloem tissue and in a few <WSD>thick</WSD> 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:  not thin; of a specific thickness or of relatively great extent from one surface to the opposite usually in the smallest of the three solid dimensions