Sentence:  The concentration and apparent localization of the WTV antigen in pseudophloem tissue of the tumor may indicate that the virus preferentially multiplies in the <WSD>phloem</WSD> and may need to be directly placed in this tissue in order to infect plants . 
Meaning of the word marked with <WSD> tags:  (botany) tissue that conducts synthesized food substances (e.g., from leaves) to parts where needed; consists primarily of sieve tubes