Fall foliage

Within these pages, we will explore the magic inherent in chemistry— from the fascination of fall foliage and fireworks, to the functioning of smoke detectors and computers, to the fundamentals of digestion and combustion— and we ll illustrate these precepts with hands-on... 

So now we have demonstrated that fireworks and fall foliage have something in common, and batteries and bumpers have something in common. But in this chapter, we have grouped all four together, so what do fireworks, fall foliage, batteries, and bumpers all have in common The answer Solar energy. 

Before windsurfing became a big hit, Hood River was famous among epicureans for its orchards and vineyards. The area s fruits are coveted by gourmet chefs worldwide. In the autumn, take a drive down the Mt. Hood Loop tour and stop at any of the fruit stands along the way. Another way to enjoy the local bounty is to visit the Hood River Harvest Festival held in mid-October. Pick up locally grown winter pears, Bartletts, Newton apples, cherries and peaches amid a backdrop of colorful fall foliage. Admission to the festival is free. 

In the fall, the chlorophyll in leaves is lost, and the red and yellow colors of the accessory pigments become visible, accounting for fall foliage colors. 

Flavonoids are the major water-soluble pigments in plants and are contained within the cell sap of plant tissues. The term flavonoids is derived from flavus (yellow) and refers to a diverse group of water-soluble pigments. Of all the flavonoids, the anthocyanins have the greatest importance from the standpoint of practical TLC. The anthocyanins are responsible for the variety of colors associated with autumnal (fall) foliage and with the variety of colors (mainly reds, scarlet, blues) associated with flowers and fruits. The anthocyanins yield anthocy-anids and various sugars upon acid hydrolysis. During the TLC of anthocyanins, it is the anthocyanids that are detected. 

All of the brilliant colors of fall foliage have one thing in common. The colors of fall are caused by molecules that contain conjugated unsaturated systems. 

Moreover, the LAI in nearly all crops is in reality above 2, primarily in the range of 3 to 5, especially in high growing crops. Correspondingly, the foliar residue will be lower by a factor of 3 to 5 (i.e., 5 pg/cm2 divided by 3 to 5 = 1.66 to 1 pg/cm2). If the crop does not cover the sprayed area completely (e.g., in row crops), then the theoretical calculation of the foliar residue still holds true, at least for conventional spraying equipment, as a proportional part of the spray mixture will not reach the foliage but will fall down to the soil. 

In fall and winter, canker bacteria, spread by rain-splash from the leaves, enter twigs through leaf scars to cause canker lesions. In spring and summer the foliage is attacked, but no new cankers are formed. 

Honeydew honey is produced not from floral nectar but from the sweet liquid excreted by plant-lice (Aphididae), jumping plant-lice (Psyllidae), and bark-lice or scale-insects 0Coccidae). These insects feed on plant juices and their excretions fall on the foliage of trees like dew, hence the term honeydew. ... 

Chemical harvest aids are presently used on more than 75% of the cotton acreage in the U.S.. The amount of foliage may be reduced either by the use of defoliants or the use of desiccants. Defoliants induce leaf fall and must be applied one to two weeks before harvest so that the abscission process may be complete. Desiccants cause the foliage to lose water and sometimes the leaves and stems are killed so rapidly by desiccants that an abscission layer has insufficient time to develop and the drying leaves remain attached to the plant. Desiccants usually require one to three days to act before harvest can be started. The obvious advantage of desiccants over defoliants is that they may be applied at a later date, thus gaining additional time during which the leaves continue to function and to contribute to see the fiber quality. Hundreds of chemicals have been evaluated as defoliants and desiccants. Only a few are in commercial use. 

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