[Grovenet] A bit of phun with physics . . . . . .

[David Morelli]

Nice post.  I've got some plants with some great red leaves for your  
house decoration.  You are welcome to pick all that you want.  They  
include berries and are quite recognizable for their three leaf  
clusters.  The leaves look a lot like oak.

<smile>
David

On Sep 28, 2006, at 5:32 PM, Bob Browning wrote:

>> The Science Behind Fall Foliage
>> By WeatherBug Meteorologist, Adam Bell
>>
>> After months of heat, humidity and ongoing drought, the time has  
>> come for summer to gracefully step aside. In its place the  
>> spotlight shines on autumn, a season renowned for cooler  
>> temperatures and the return of football. However, while attending  
>> a football game in the chilly weather can be invigorating after  
>> the stifling summer heat, that's not all the Fall season has to  
>> offer. Another popular feature of the post-summer months is the  
>> fall foliage.
>>
>> Starting in mid-September and lasting until early November, the  
>> changing leaf colors can be seen in the Pacific Northwest, the  
>> Rockies, Midwest, Ohio Valley, the eastern mountains as well as  
>> the mid-Atlantic and the Northeast. With these changes arriving  
>> very soon, let's take a look at what makes those leaves change color.
>>
>> First things first, why are leaves green during the spring and  
>> summer? One word: chlorophyll. This green pigment is abundant in  
>> leaf cells during the growing season. As a result, the  
>> chlorophylls' green color masks out any other pigments in the leaf.
>>
>> In order to understand the changing fall colors, we must learn how  
>> the leaf works. In addition to giving leaves their green color,  
>> chlorophyll also captures the sun's energy. Chlorophyll utilizes  
>> this energy to split water molecules, brought into the leaf via  
>> the roots, into hydrogen and oxygen atoms. Meanwhile, tiny pores  
>> on the surface of the leaf, called stomata, take in carbon dioxide  
>> from the air. Once the carbon dioxide reacts with sugars in the  
>> plant, it too is broken down to its simplest parts, carbon and  
>> oxygen.
>>
>> After all of the compounds have been simplified, the leaf begins  
>> the reconstruction process. Individual atoms of carbon, hydrogen  
>> and oxygen are joined together to make glucose, an energy-rich  
>> sugar that nourishes the plant. For every molecule of glucose that  
>> is produced, there are six molecules of oxygen leftover. The  
>> stomata release this gas into the air we breathe.
>>
>> This process, called photosynthesis, tends to destroy the  
>> chlorophyll. But the warm temperatures and strong incoming solar  
>> radiation during the spring and summer helps to create more  
>> chlorophyll to replace what is lost. Because the chlorophyll is  
>> constantly replenished, the green pigment is always present in the  
>> leaf, keeping the tree green.
>>
>> That's all well and good, but what gives the leaves that  
>> unmistakable fall color? During the autumn season, the Northern  
>> Hemisphere starts to tilt away from the sun. This shortens the  
>> window of daylight, which in turn lowers the temperatures. As this  
>> cooling takes place, a thin layer of cells, located at the  
>> junction of the leaf and stem, begin to swell and form a cork-like  
>> substance. This swelling cuts off the supply of water from the  
>> roots, thereby taking away one key ingredient of photosynthesis.
>>
>> Another important part of photosynthesis, the sunlight, is also in  
>> short supply due to the Earth's tilt. The lack of water and  
>> sunlight halts the photosynthetic process and therefore ceases  
>> chlorophyll production. With this absence of chlorophyll, other  
>> pigments in the leaves finally have a chance to come forward.
>>
>> One such pigment is carotenoid. Responsible for the yellows,  
>> oranges, browns and hues in between, carotenoids are also found in  
>> familiar foods. Corn, carrots and bananas are just a few that are  
>> colored by this pigment. Like chlorophyll, the carotenoids are  
>> present in the leaf cell during the entire growing season. The  
>> similarities stop there, however, as the concentration of  
>> carotenoids is much less than that of chlorophyll. Some species of  
>> trees that have higher amounts of carotenoids include hickories,  
>> birch, poplar, sugar maple and black maple.
>>
>> The reds and purples come from a pigment called anthocyanin. It  
>> too adds color to foods such as cranberries, red apples, cherries  
>> and strawberries. In contrast to chlorophyll and carotenoids,  
>> anthocyanins are not always present in the leaf cell. Their  
>> formation is dependent on low levels of phosphate in the leaf.  
>> Because there is a high level of phosphate during the growing  
>> season, the production of anthocyanins must hold off until that  
>> level drops, usually around late summer. A few trees that produce  
>> red and purple leaves in the Fall include the dogwood and the red  
>> maple.
>>
>> Weather plays a very large role determining how vibrant the fall  
>> color will be. A warm, wet period during the autumn will decrease  
>> the brightness of the foliage. A severe frost early in the season  
>> will likely kill the leaves, turning them brown and causing them  
>> to fall from the tree. Severe drought could delay the fall colors  
>> by two to three weeks.
>>
>> So what are the weather conditions for great fall foliage? While  
>> there is no magic recipe, the best colors tend to be seen when  
>> there is a warm, rainy spring, a summer that is not brutally hot  
>> and a fall season with sunny days and crisp, cool nights.
>>
>> Since a few of the northern states are already reporting signs of  
>> fall color, now is the time to start planning that foliage drive.  
>> For those who have never driven through the changing colors, you  
>> should make an attempt this autumn as the trip is truly scenic.
>>
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