Tension wood, one of the two types of reaction woods, is commonly differentiated on the upper side of leaning main stem regions and laterally disposed branches of dicotyledonous trees. It is considered by many to be the response to gravitational stress. There are also reports of its involvement in the efforts of the plant to correct the leaning portions of the main trunk. The present study is aimed at finding out whether the differentiation of reaction wood is related to the maintenance of the branch angle irrespective of the age and increased mass of the leader branches in Eucalyptus tereticornis. This species shows an almost constant branch angle in the range of 50 degree to 60 degree in all its leader branches, irrespective of their age. The quantum of differentiation of reaction wood as well as the linear dimensions of its constituent gelatinous fibre were estimated in different regions of all lateral branches from base to tip. The results are discussed in order to highlight the role of reaction wood in maintaining the canopy geometry of this taxon.

Key words: branch angle, crown geometry, Eucalyptus tereticornis, gelatinous fiber, tension wood