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Donald R. Kaplan
Published 1984 · Biology
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This article examines the question of alternative modes of organ development in higher plants, taking its examples from convergences in dissected leaf form that are produced by different morphogenetic programs. In Araceae leaf dissection occurs either by conventional marginal lobing, as in the pinnate leaf of Zamioculcas , or by localized tissue death as in the perforated leaf of Monstera. In the palms, both palmate and pinnate leaves originate by a process of intralaminar corrugation followed by a cleavage of the resultant pleats into the free lobes or leaflets. The origin of plications has been the most controversial aspect of palm leaf development. Some workers suggested that this pleating arises by differential growth or meristem folding while others have supported a tissue cleavage process. By a detailed, comparative morphological and histogenetic analysis of plication inception and early growth in the pinnate leaf of Chrysalidocarpus lutescens and the palmate leaf of Rhapis excelsa , it could be shown that plication origin in both taxa occurs by differential growth rather than by tissue cleavage. It is concluded that the principal reason for this difference in past interpretation was the reliance of previous workers on matters of plication shape for the determination of the developmental mechanism involved. By using a quantitative evaluation of the cellular basis of plication origin we were able to transcend matters of shape and show that plication configuration in the respective species is a consequence of physical constraints within the leaf itself or between leaves in the bud rather than different morphogenetic mechanisms. It is emphasized that in future researches greater attention should be directed toward the determination of the common denominators of such different developmental programs rather than the mere cataloging of their superficial differences.

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