This paper is a report of an anatomical research undertaken in 1947 on the trunks of mature sweet orange trees on sweet orange rootstock. Object of the investigation was to determine the time at which new trunk phloem is produced, with respect to the time of shoot and root extension growth and xylem production. Also investigated were the anatomic features of xylem and phloem development; the portion of the phloem which is replaced during the year; and how and when the older sieve tubes degenerate.
