Abstract: The dormant cambial zone consisted of 5–6 cell layers in the main stem of Pinus sylvestris L. trees that were ca. I00 years old. Time of cambial reactivation was comparable at one (bottom) and 8 (top) meters above the ground. In spring, when the cambium reactivated, the number of cambial cells slightly increased and phloem cells were formed. The production of xylem cells followed 3–4 weeks later. The formation of xylem cells decreased, whereas that of phloem cells increased between late June and early July. Cambial reaction in 1-year-old cuttings that were debudded and treated apically with IAA in lanolin was similar to that in the ca. 100-year-old main stem. However, in debudded cuttings treated with plain lanolin, the number of cells in the carnbial zone decreased during the first week of culture, and only a few phloem cells were formed. Later, the fusiform cambial cells of the cambial zone were divided transversely and lost their typical morphology. It is proposed that some factor(s) from roots may stimulate the initiation of cambial cell division, because when the cambium reactivated, the number of cambial cells slightly increased in the ca. 100-year-old main stem, but decreased in the 1-year-old cuttings.

Key words: Pinus sylvestris, Cambium, IAA