The Annual Rhythm of Activity of the Lateral Meristems (Cambium and Phellogen) in Pinus Halepensis Mill. and Pinus Pinea L.

Abstract

The annual rhythms of cambial and phellogen activity in Pinus halepensis and P pinea were investigated. Under natural conditions the cambium of P halepensis begins its activity in autumn, enters a quiescent period during midwinter, resurnes activity towards spring and enters a second rest period in summer. The ring border is formed during summer. Irrigated plants growing outdoors were active almost all the year round. The cambium of P pinea is active between April and November and enters a true winter dormancy. The duration of xylem production exceeded that of the phloem. More xylem than phloem cells were formed. The phellogen was active during a short period only. Pinus halepensis seems to follow the Mediterranean climate patterns whereas P pinea follows the pattern of a colder climate.