It is useful in studying plant development requiring destructive measurement on multiple individuals.
By measuring a metric against morphological age, instead of chronological time, one can reduce variations occurring between individuals, thus allowing greater focus on variations due to development.
[1] The leaf plastochron index, also referred to simply as the plastochron index (PI) as it is derived from, is a demography formula used to determine the developmental age and growing rate of a leaf or other growing plant organ.
[2] This formula was useful when first introduced as it allowed scientists to be able to track the progression and growth of a plant.
According to American Journal of Botany, the typical variation of the formula for the plastochron index is as follows;
The following is the key to use the typical variation of the formula; “n” is the leaf's sequential index (or serial) number.
However, when using the formula supplied by the American Journal of Botany there are multiple assumptions or requirements of the leaf that is being studied for the calculation to be accurate.
Erickson and Michelini dictate that the “organ growth must be exponential” meaning the leaf must be growing.
Also, “successive organs must be growing at the same relative rates” meaning the measurement will not equate to other plant growth unless they share the same growth rate even if they are co-dependently growing.
Finally, “Successive plastochrons must be equal, where here, plastochrons are defined as the time intervals between the attainment of length R by successive organs” meaning that some research of the leaf's reference length is needed for the formula to be verifiable.
[3] In Burström's variation, he uses a Xanthium plant as an example which was 10 mm (thus, why 10 was used as the reference unit).
A cottonwood leaf was the organ used for this research as this plant has uniform rates of growth, meaning it falls under the requirements needed for the formula's verifiability.
This study shows how the leaf plastochron index can be used within scientific research to explore and predict certain developmental events of a leaf or other plant organ's life cycle through a non destructive method of morphological feature identification.
Botha and R.J. Strasser's South African Journal of Botany article A re-evaluation of plastochron index determination in peas -- a case for using leaflet length.
For this study the following variation of the leaf plastochron index formula was used;
This study was conducted in order to determine whether the leaf plastochron index works for pea plants (Pisum sativum).The researchers’ results showed that the pea plant (Pisum sativum) met all the requirements needed to use the leaf plastochron index formula in a verifiable manner when finding plastochron age through leaf length.
This shows that the leaf plastochron index can measure successive pairs of leaflets in pea plants (Pisum sativum).
[2] Although Erickson and Michelini were responsible for introducing the formula, the concept of the plastochron being used as a unit of measurement was inspired by scientist Askenasy originally in 1880.
[7] He received an education from Gustavus Adolphus College in 1939 and Washington University in St. Louis where he inevitably attained his Ph.D. in 1944.
Although he first began teaching at Rochester in 1944 until 1947, much of his career was spent at the University of Pennsylvania where he received his professorship between 1949 until 1985.
The plastochron index has now been used by many authors, including [themselves], in a variety of ways.” He later went on to receive his Guggenheim Fellowship for his work in plant physiology where he used the plastochron index in order to determine and assess the temperature and light effects on the developmental growth of the plants.
He received an education at Seton Hall College, the University of Delaware and the University of Pennsylvania where he received his Doctorate of Philosophy degree in Biological science.
[9] He began his teaching career at Wilkes College and received his Professorship of Biology in 1963.
In 1957, Michelini published his article The Plastochron Index with Ralph O.