April 2019 Limerick Project


“Within all the plant life arboreal,
Reactions— complex, inventorial—
Cause synthesis (photo);
Roots extending below,
Long relics of time immemorial.”

The last of the poem homages was published on 26 April 2019, a date on which the Friday of Earth Week and Arbor Day overlapped.  It took as its central image the famous setting from the first line of Henry Wadsworth Longfellow’s “Evangeline.” As with most of the poems in this sequence, the allusion was a surface one at best: the “forest primeval” simply seemed a fitting theme for Arbor Day!

“Within all the plant life arboreal, /
Reactions– complex, inventorial– /
Cause synthesis (photo)…”
In teaching my classes, I focus on simplified scenarios in which chemical reactions occur one at a time and can be easily tracked and understood.  In any real-world system, the underlying chemistry is multifaceted, consisting of multiple processes occurring in tandem (“reactions– complex, inventorial”).  Photosynthesis is the process by which trees and other plants (“the plant life, arboreal”… and otherwise) can convert the energy from sunlight into chemical energy; it has enormous implications for life on earth, including the generation of oxygen.  Describing photosynthesis comprehensively requires a large number of interconnected chemical reactions. 

“Roots extending below, /
Long relics of time immemorial.”

A reaction’s “timescale” defines how quickly it can occur.  Again, in teaching, I highlight reactions that occur over a scale of seconds to minutes; these can be easily monitored in a classroom environment.  However, reactions can occur much more slowly and much more quickly.  Scientists sum up these timescales with the use of metric prefixes: some processes can take months or years (megaseconds); others can occur in a billionth or a trillionth of a second (nanoseconds or picoseconds, respectively).  

Within a tree like an ancient sequoia, multiple timescales are impressively, simultaneously evident, given the trees’ massive scales and lifetimes through centuries, via these cascades of chemical reactions, continuously occurring in fractions upon fractions of seconds. In her outstanding memoir Lab Girl, Dr. Hope Jahren writes movingly about the chemistry and drama underlying botany: “No risk is more terrifying than that taken by the first root.”  Centuries later, far outpacing our own timescales, these “long relics” can persist.