“Opposite”

“Phyllotaxy” is the arrangement of leaves on a plant stem; apparently from Greek phýllon “leaf” and táxis “arrangement.” This image from the genus Plectranthus is an obvious example of the “opposite” arrangement.

From “Twig and Leaf Phyllotaxy,” by Carol Levine (Newsletter of the Connecticut Botanical Society. Fall 2000, volume 28, no. 2 & 3), http://www.ct-botanical-society.org/newsletter/phyllotaxy.html »
“Leonardo da Vinci once wrote ‘The leaf always turns its upper side towards the sky so that it may be better to receive the dew over its whole surface; and leaves are arranged on the plants in such a way that one covers another as little as possible. This alternation provides open spaces through which the sun and air may penetrate. The arrangement is such that drops from the first leaf fall on the fourth leaf in some cases and on the sixth in others.’ This observation call[s] attention to the fascinating, naturally occurring mathematical phenomena: leaf phyllotaxy and the Fibonacci numbers.

“Leaf phyllotaxy explains how leaves are arranged on the twig, why they are opposite, whorled or alternate:

» “Opposite leaves have the leaves opposite in respect to each other, and usually the adjacent tiers cross at right angles to the original opposite leaves. This is described as opposite-decussate, or pairs alternately crossing at right angles.”
» “Whorled means three or more leaves at one node.”
» “Alternate leaves are distributed along the twig in a spiral. If we draw a line from the point of attachment of one leaf to the next, this line will wind around the twig as it rises. The same species will always bear the same number of leaves for each turn around the twig. An equal portion of the circumference of the stem will always separate the successive leaves from each other. Thus is created an equiangular spiral.”

Genus page at PhytoImages, http://phytoimages.siu.edu/cgi-bin/dol/dol_terminal.pl?taxon_name=Plectranthus&rank=genus

Photo taken at SIUC Plant Biology Greenhouse, http://www.plantbiology.siu.edu/facilities/plant-biology-facilities/greenhouse/index.php

1 year ago (“More sharp objects…”): http://365project.org/rhoing/365/2013-02-25
2 years ago (“Got mud?”): http://365project.org/rhoing/365/2012-02-25
3 years ago (“A Brief History of Computing”): http://365project.org/rhoing/365/2011-02-25

25th February 2014 25th Feb 14