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N. Venugopal and K. V. Krishnamurthy

Secondary xylem production in four deciduous (Albizzia lebbeck, Dalbergia sissoo, Tectona grandis, Terminalia crenulata) and three evergreen trees (Calophyllum inophyllum, Mangifera indica, Morinda tinctoria) is briefly described. The total duration of xylem production in a year has been analysed. In three of the four deciduous trees there were two periods of xylem production in correspondence with the presence of two flushes of cambial activity and sprouting of new vegetative buds and foliage formation . In Tectona grandis and in all the three evergreen species studied there was only one period of xylem production. Periodicity in the production of different components of xylem tissue as well as the difference in the dimensions of the different xylem elements produced during each flush of cambial activity resulted in detectable growth ring boundaries within the xylem. Conspicuous changes were found in the starch and crystal contents of xylem cells adjacent to the cambial zone during the initiation and cessation of cambial activity .