Plant Biology

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Offline andreparis

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Plant Biology
« on: 25/07/2005 04:51:32 »
How was plant biology discovered?  As in, how did modern science figure out what processes go on inside a plant?


Offline Andrew K Fletcher

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Re: Plant Biology
« Reply #1 on: 25/07/2005 07:55:51 »

You may find the previous thread on this subject to be of interest. As for the origin of the subject of Biology, I have no Idea where it all started. But ignoring physics is where it all went wrong :P

Andrew K Fletcher

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Offline finchbeak

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Re: Plant Biology
« Reply #2 on: 01/08/2005 14:30:38 »
Andrew - the thread you reference does not include anything about the history of plant physiology.  I will post to that thread later, but I can tell you that it is very common for physicists to scoff at the cohesion-tension theory upon first hearing it.  I assure you, when you look at the details, you will see that no physical laws are violated and that plant biologists do not ignore physics.  Indeed, all good plant physiologists are deeply steeped in physics, whereas very few physicists can claim to be anything but deeply ignorant of plant physiology.  This is not a slight on physicists, by the way; it simply reflects the fact that plant physiology relies heavily, as it should, on physics, while the reverse is not true (until one realizes that all physicists, being animals and therefore aerobic heterotrophs, are utterly dependent on the physiological processes going on in plants).  :P
Andre - as in all sciences, the development of the field we now call Plant Physiology has been a long, slow process.  Some of the earliest experiments in the field were performed by Joseph Priestly in the late 18th century.  He discovered that a candle under a bell jar would remain alight longer if a plant had previously occupied the jar for a few hours.  In a similar experiment, he discovered that a mouse placed under a bell jar would live longer (before suffocating) if it shared the bell jar with a plant.  In fact, he found that a reasonably large, healthy plant could sustain a mouse indefinitely.  Of course, Priestly interpreted these results in light of the then-popular "phlogiston" theory.  Essentially, he believed that fire and the breathing of animals somehow "injured" the air and that plants have the ability to restore it.  We now understand these results in terms of oxygen, carbon dioxide, and photosynthesis.  Priestly's papers are marvelous reading, by the way.  I can send you a copy if you like.
Another experiment performed around 1800 (I can't remember the investigator offhand... I'll look it up) asked the question of where a plant's mass comes from.  A tree seedling was planted in a pot and the whole thing was weighed.  Over the course of a number of years, the plant grew and the investigator was very careful to add nothing but water to the pot - no additional soil or nutrients of any sort, only water.  Well, of course the plant + soil + pot gained a lot of mass.  Where did the mass come from?  The investigator reasonably (though quite mistakenly) concluded that all of the mass must have come from the water, since that was the only substance added.  He thus concluded that plants have the ability to somehow transform water into leaves and wood and other planty bits.  We now understand this conclusion to be utterly wrong; in fact, nearly all of the mass accumulated by a plant comes from the air, specifically in the form of carbon dioxide.
Another famous series of experiments was carried out by none other than Charles Darwin and his son Francis.  They were among the first investigators of the phenomenon called phototropism - the bending of a plants parts toward or away from light.  The Darwins found that the curvature of an oat seedling toward light was caused in an interesting way: the very tip of the seedling was involved in sensing the direction of light although the actual curving of the stem occurs somewhat further down.  They concluded that there must be some substance produced at the tip that travels downward and causes the bending effect at a distance.  This was the first indication the plants have growth regulators - now called plant hormones.  
Of course, the well-known experiments of Gregor Mendel are an excellent example of an early advance in our understanding of how plants work.  
These are some examples of early work in the field of plant physiology.  The twentieth century saw [weird to speak in the past tense about the 20th C] a great increase in interest in plant biology.  You can find a lot of historical information in most basic botany textbooks.