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The plastochron index and the leaf plastochron index are ways of measuring the age of a plant dependent on morphological traits rather than chronological. This will erase germination and developmental differences and exponential growth.
In 1951, F. J. Richards introduced the idea of the plastochrone ratio and developed a system of equations to describe mathematically a centric representation using three parameters: plastochrone ratio, divergence angle, and the angle of the cone tangential to the apex in the area being considered
References
- FJ Richards, Philos. Trans. R. Soc. London, Ser. B 235, 509 (1951).
A plastochron refers to the rate of initiation of undifferentiated primordia while a phyllochron is the rate of emergence from the apical bud. Emerging phyllodes or leaf variants are suddenly changed from a high humidity environment to a more arid one. There are other changes like light level and photoperiod and gaseous content of the air. Some such effects on phyllochron/plastochron ratio are discussed in: Effects of Higher Temperatures, Photoperiod and Seed Vernalisation on Development in Two Spring Wheats by H. M. Rawson and M. Zajac Aust. J. Plant Physiol., 1993, 20, 21 1-22 Rawson and Zajac A functional-structural model of the elongation of the grass leaf and of its relationships to the phyllochron by C. Fournier, J.L. Durand*, S. Ljutovac, R. Schäufele†, F. Gastal* and B. Andrieu Fournier etal
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