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Résumé :
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Growing leaves of tall fescue (Festuca arundinacea Schreb.) were studied from emergence to a short time before the leaf ceases growth. Leaf form (width, average thickness, number of vascular bundles and height of associated ridges) and growth patterns were determined. The tissue elements produced at the point of leaf insertion are wider and thicker with time, as the intercalary meristem develops. These elements undergo further width and thickness changes as they traverse the elongation zone, and leaf width and average thickness can continue to increase after passing the elongation zone. In order to relate the generation of leaf form and dry matter (DM) deposition, three methods were used to describe DM fluxes: (1) we followed the path lines of material elements and determined that they accumulate DM as they are displaced away from leaf base, even when expansive growth and maturation are complete; (2) we calculated DM deposition on a unit length basis, which represents the total sink strength of the zone studied, and we deduced that the sink strength of the elongation zone increases with time, in concert with the changes in width and thickness of the elements that are successively produced at leaf base; (3) we calculated DM deposition on a unit volume basis, which represents the net metabolic activity of the zone considered, and we found that growth activity and associated DM deposition were high 3 d after the leaf emerged, then decreased gradually, whereas maturation and associated DM deposition were low at emergence, but increased as the leaf gradually became autotrophic. Our data indicate that different descriptors and measurements are needed during the totality of leaf growth. (C) 1997 Annals of Botany Company.
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