1. Formation of growth rings

In a temperate climate marked by seasonality, trees produce an annual ring during the period of vegetative activity (April to September, in the northern hemisphere), by periclinal division of the cambial base located at the periphery of the organ, beneath the cortical tissue.

In conifers (gymnosperms), the ring consists of (figure 1 a and 1 b ):

• a light initial wood (low density, with wide tracheids and thin walls) that forms in spring;

• a darker final wood (higher density, with small, thick-walled tracheids) that forms in summer and early autumn.

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