EVERGREEN NEEDLES - STRUCTURAL ASPECTS OF HEALTHY AND DAMAGED NEEDLES

In evolutionary terms the conifers are substantially older than the an giosperms, and their approx. 500 species comprise fewer than 1% of all tree species. Nevertheless they compete successfully with the more '' modern'' angiospermous trees over one-third of the world's forest area . This is due primarily to the physiological efficiency of their frequ ently evergreen needles, which are adapted to cold, drought, and short vegetation periods. The underlying structures are described in some d etail, and it is demonstrated how direct or indirect changes due to th e impact of abiotic stress factors may impair the complex interactions of cells and tissues.