A description of the wood structure of Prosop is flexuosa DC. (Legum.) is given. It is semiring-porous, shows pores solitary, in multiples and in clusters; small to large-sized vessels with simple perforation plates, and thick vessel walls. Rays multiseriate and homogeneous. Paratracheal axial parenchyma and libriform fibres. The hydraulic tissue seems well adapted to very low rainfall and prolonged dry periods. Seasonal variations in cambial activity have been investigated from July 1982 to

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... e 1984. Prosopis flexuosa has an annual rhythm of wood production which coincides with the climatic rhythm. Cambial activity is initiated in the last week of October, reaches a peak in November/December and ceases in April. The initiation time in the activity of vascular cambium seems to be endogenous. A dormant period was noted when defoliation takes place during the dry months. Relationships between xylem production, phenology and climatic factors are discussed. Although the growth rings are not always clearly demarcated, one growth ring is generally formed each year.