L'evoluzione della cerchia legnosa in Pinus halepensis Mill. in Bari

Summary

The evolution of the wood ring in Pinus halepensis M'ill. in B'ari (from july ′46 to july ′47).

The present study deals with the anatomical characters of the wood-ring in the Aleppo pine, in a grown-up specimen (80–100 years) and in a young one (20–25 years); in both the specimens the wood of the stem and of the young branch has been investigated.

The wood elements forming the ring are more highly differentiated, respectively in early and late wood in the stem of the grown-up specimen in comparison with those of the stem of the young one, and respectively the wood ring of the young branch shows a lower stage of differentiation in comparison with that of the stem of the same specimen; so that the older a specimen or a part of a specimen, the higher the degree of differentiation of the parts of its wood ring; namely the early tracheids are more different from the late ones. Conclusively, the final histological aspect in the secondary wood of the Aleppo Pine seems to be attained rather late.

A parallel physiological arrangement, during the tree life, seams to be reached by this species. In the grown-up specimen the cambium starts dividing in the young branch about one month earlier than in the stem, while in the young specimen the cambium begins its divisions about conteporarly both in the branch and the stem. In both the grown-up and the young specimens the cambium initiates its radial growth about one month before the unfolding and elongating of the vegetative buds. All these facts lead to the hypothesis that a cambial moltiplication stuff might be elaborated during the preceeding season and might be stored near the cambium, being so responsible of the awakening of the cambial activity, before the bud unfolds at the new season.

This division stuff ought to be stored along the whole axial part of the young specimen, while in the grown-up one its storage should be limited to the young branches only, where it will stimulate cambial division next spring.

Owing to the correlation between cambial activity and climate factors, in the specimens, cambial activity begins about half March in the branch and half April in the stem, namely about one month later than in Palestine, probably in dependence of the different winter temperature between the two countries.

The early wood is formed from April to May-June with a sudden start in the grown-up specimen, more slowly in the young one. In July the differentiation of the late wood begins—This date seams to be rather constant, as I have observed exactly the same stage in the wood ring of July 1946 and in that of July 1947, while the two preceeding Spring times had different rainfall quantities, namely the Spring 1946 had been rather dry, while the Spring 1947 rather wet. The cambium goes on settling late wood elements as late as December, January and probably February, with a discontinuous path, and this portion of the ring is the most critical one, revealing in its characteristics the climatic behaviour during the summer and autumn time.

In conclusion the two different parts of the wood ring start and stop their formation in rather fixed seasons, so that the quantity rather than the quality, of the wood formed, reflects the climate of the period, during which the corresponding portion of the wood ring has formed.