Xylem and phloem formation in chestnut (Castanea sativa Mill.) during the 2008 growing season.

Abstract: Cambial activity and the dynamics of xylem and phloem formation were monitored during the 2008 growth season in five chestnut (Castanea sativa) trees growing near Viterbo, Italy. The study was based on microscopic observations of micro-cores taken from stems at weekly intervals from mid-April until mid-October 2008. These observations allowed us to identify the timing of xylem and phloem formation. Cambial divisions, xylem and phloem formation had already started before the first sampling. By the end of April, the first earlywood vessels were already lignified and in early phloem the first formed sieve cells had finished postcambial growth. Formation of earlywood was completed by the end of May, which was about 2–3 weeks earlier than the completion of early phloem. The highest production of xylem cells was recorded between mid-May and mid-June and of phloem ones from mid-June until mid-July. Wood and phloem production mainly terminated in the middle of August while differentiation of xylem cells lasted until mid-October. The phloem ring was completed by the beginning of October 2008. Xylem growth rings were on average 2027±635μm wide and phloem rings 265±68μm. The proportion of latewood was 73±8% and of late-phloem 49±11%. [Copyright &y& Elsevier]