MUELLER, RICHARD J. Department of Biology, Utah State University, Logan, UT 84322. - Using the plastochron index to improve student’s understanding of exponential plant growth and the use of logarithms.
The plastochron and leaf plastochron indices are methods created by
R.O. Erickson and F.J. Michelini in 1957 to measure the age of whole
plants and individual leaves based on their morphology rather than
chronological age. They have been particularly useful for detailed
studies of whole shoot and leaf development. Since the indices are
based on measurements of exponential plant growth, they provide an
opportunity to demonstrate the value of applying mathematics to a
biological problem. I will describe a laboratory exercise from a
upper-division Plant Structure course in which students are presented
with the theoretical basis of the indices and then calculate them for
Xanthium strumarium (cocklebur) plants of various ages (4-6
weeks). The exercise demonstrates both the potential variability in
plant growth and the results of an exponential growth rate. Pre- and
post-tests showed a significant increase in the student’s
understanding of exponential growth and their ability of work with
logarithms. This exercise was created as part of the BioMathLab
project at USU supported by Department of Education FIPSE grant P116B
71688.
Key words: Xanthium strumarium, exponential growth, plastochron index, shoot development