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08 August 2003

The Effect of Photoperiodicity on the Fruiting of Maple Trees

by James Farr

Connecticut,1972

As a High School student I was required to read Charles Darwin. One thing that intriqued me was the simple way he presented the Theory of Natural Selection. The book Origin of Species was filled with examples of how an organism was found that seemingly, through the struggle to survive, out competed neighboring or closely related organisms, and then evolved into something different.

Darwin explained the process as being through sheer competition, which I still agree with today. However there were other ways organisms could evolve.

One good example is through complex chemical interactions associated with light stimuli. In fact, Darwin himself spent an enormous amount of time studying plant tropisms. He concluded plants grew towards light because a chemical was reacting to the sunlight's intensity through his laboratory window. Therefore, my question was, how complicated is that chemical reaction leading to tropisms in plants? I decided to conduct an experiment. I was going to predict the time Maple trees bloomed on our campus two successive years. My first purchase was the l972 Old Farmer's Almanac. That was a real tool that I could use to both set up the experiment, and then log the parameters (i.e., moisture, temperature, sunlight) that would affect the tree's blooming.

Although I don't have the actual figures I kept I recently looked up the old 1972 edition of the Old Farmer's Almanac. This edition suddenly reminded me how well planned that experiment was.

In the winter of 1971, there was little snow, and by June when the trees usually fruit the temperature was warm early. I remember seeing the fruiting maples on a warm, humid day in late May. That entire month was warm. The maples had fruited earlier than usual.

In the Almanac it was recorded that the next winter would be wet, as well as colder with more snow. Therefore, by all probability the trees would fruit in early June rather than late May.

I remember peering out my window waiting fror the trees to fruit in June, 1972. Most years I was there in Connecticut, I would see the fruiting before leaving campus. However, their fruiting was so delayed in 1972, I had to leave school for summer vacation without actually seeing it.

One problem that arose was that those two winters were quite different from one another. The winter of 1972 had a total of 42.9 inches of precipitation. The winter of 1972, as predicted by the Almanac, had 22.1 inches.

Yet there were other factors in play. First, there was a lunar eclipse at about the time the l972 maple tree fruiting occurred.

The difference in moisture seemed to me not the real reason for the late fruiting in l972. Actually the higher precipitation, almost two times the usual quantity, occurs many years, and really didn't seem to me to be a real factor influencing the tree's fruiting.

I began to think photoperiodicity was the answer. In fact I repeated some of Charles Darwin's experiments in my biology class. I covered a certain part of a flower stem with aluminum foil, exposing only the very tip to light. I had a control experiment, covering the tip only with the foil. Darwin was right, there must be a chemical allowing that plant to bend towards light. The chemical must be near the base of the stem of the young fruit. Those chemicals are plant hormones. The first set of those hormones was discovered in the l950's.

The complexity of that chemistry is utilized quite well by fruit tree growers. For an unknown reason, spraying orange trees with a little ethylene causes fruit to drop. There is a chemical association with the ethylene and the hormone, which hastens the ripening of the fruit.

This type of chemistry is really the chemistry of physics and to this day is not clearly understood.

Recently I saw in our local Newspaper an article that a amateur biologist in our area claims that the light illumination from buildings were influencing the breeding of blue-claw crabs. He goes fishing every night at three AM, for Striped Bass. He usually fished when blue-claw crab larvae, or cinder worms are abundant. He has found that the cinder worm presence has lessened. Thus the catches of striped bass are being reduced. The biologist also takes notes about weather conditions, illumination, water temperature and salinity. He hopes to prove that illumination from nearby buildings are slowly defeating nature's ability to grow Striped bass and Blue-Claw crabs. I wish him luck. Studying photoperiodicity is one of the most complex subjects one can approach in biology. You have to be very sure about your data and have an enormous quantity of it. Most plants and animals have an intrinsic clock where illumination is patterned deep in our metabolism. We react to sunlight quite unaware of its subtle effects. There is really (in my opinion) no answer to the effects of photoperiodism on animal or plant breeding or ecology. It is too complex.