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The Plastochron index in Developmental Studies of Xanthium italicum Moretti

Francis J. Michelini
American Journal of Botany
Vol. 45, No. 7 (Jul., 1958), pp. 525-533
Stable URL: http://www.jstor.org/stable/2439575
Page Count: 9
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The Plastochron index in Developmental Studies of Xanthium italicum Moretti
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Abstract

Develepomental studies in higher plants have been seriously hampered by the difficulty of obtaining parallel samples of experimental materials. When chronological age is used as a selecting criterion in such studies, reproducibility is very limited. Recent advances in biochemical and physiological knowledge have brought an increase in the understanding of many of the specific reactions involved in growth and differentiation and makes more important the linking of these processes to development. In this study on Xanthium italicum Moretti an attempt was made to establish a relationship between various morphological stages of the developing plant and certain of its physiological activities. Leaves of Xanthium in various stages of development were collected and analyzed for fresh weight, dry weight, chlorophyll content and oxygen consumption. There was no consistent relationship noted between the developing leaf and these physiological characteristics on the basis of the selecting criteria of chronological age. Utilizing a previously established formula, the plastochron index, for expressing development in terms of leaf morphology it was found that the fresh weight, dry weight, chlorophyll synthesis and oxygen uptake of individually developing leaves followed a straight line relationship to their particular stage of growth. Interpretations of leaf morphogenesis in terms of relative rates of these variables are discussed. It is suggested that the use of the plastochron index or a comparable developmental scale may be a reliable tool in the interpretation of physiological processes and morphological changes during growth and development.

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