As stated in the previous post, bark is a mixture of living and dead cells.  Cork cells abound, especially in trees like the cork oak, where the cork may be regularly harvested.  This may be used for flooring, insulation and yes - corks for wine bottles. However, bark is a source of many things.  From early times, bark from trees like alder, buckthorn, oak, birch etc were used to make dyes for clothing.  Material from the inner bark of some trees (e.g. lime, willow, mulberry) was a source of fibres for clothing and cordage (string / yarn). Herbalists also found a use for the bark of certain trees.  Infusions of willow were used to treat fevers, the ‘ague’, rheumatic aches and pain.  It contains salicin, which the body converts to salicylic acid, an early 'form' of 'aspirin'. Interestingly, Nicholas Culpeper, in The Complete Herbal (of 1653) gives a number of uses for willow, including to staunch wounds, but does not mention pain control. The bark of the Cinchona [Jesuit’s bark] gave quinine - a treatment for malaria [caption id="attachment_39935" align="alignleft" width="300"] Amber[/caption] When a tree, like a pine, is injured (through storm damage or insect attack), the bark can produce resin - a sticky and viscous liquid.   The resin is produced in resin ducts present within the bark tissue, though the ducts may be present in deeper tissues. Research has shown that ponderosa pine trees that had more (and wider) resin ducts survived drought and bark beetle attack better.  The resin can harden and help seal wounds . Many resins contain terpenes, such as alpha-pinene and limoneme.  The resin from pine and other conifers can under special circumstances be converted into amber.  Sometimes, the resins produced can be fragrant. Trees of the genus Boswellia and Commiphora produce a aromatic resin that gives frankincense and myrrh respectively.  Both are produced by the wounding of a tree so that its resin seeps out.  Both may be used in the making of incense. Another bark exudate comes from certain species of Acacia - Gum arabic, which forms from the hardened sap (adjacent image).  Acacia species belong to the ‘Bean’ family (Fabaceae).  The gum is collected from trees, mostly in Sudan and the Sahel.  Gum arabic is a mixture of glycoproteins and polysaccharides.  The polysaccharides are constructed from the sugars arabinose and galactose. It is soluble in water and edible, and has a number of uses in the food and pharmaceutical industries. Tapping or wounding the bark of different trees can result in various fluids being released, for example, latex.    White or yellow latex is produced by the rubber tree (Hevea brasiliensis).  The latex is found in special vessels within the bark - laticifers. The process of tapping rubber trees is outlined in some detail here.   Latex production is not confined to woody trees, small herbaceous plants like dandelion and spurge can produce a white, milky latex (as can the opium poppy). [caption id="attachment_39984" align="alignleft" width="300"] Euphorbia latex[/caption] The latex produced by some members of the Spurge family can cause burning pain, inflammation or even blistering - for example that of the Pencil tree.  Such toxic saps most likely evolved to deter animals from grazing. Sometimes, a watery sap may be collected from the bark.  This is the case with Birch.  Sap may be collected (tapped) in early Spring, when sugars and other materials are being mobilised for growth, leaf production etc.  Sap may be collected later but is said to then have a bitter taste.  The sap is an interesting ‘cocktail’ of amino acids, protein, sugars (glucose & fructose), betulinic acid, proteins, vitamins C & B, and minerals.  It is used to make a much favoured drink in Northern Europe and should be consumed within days of collection.  Birch trees are quite sensitive to tapping. Not watery, but very sugary is Maple Syrup. Maple trees are tapped by drilling holes through their bark and into their trunks. Starch is stored in the trunks and roots before winter, it is then converted and mobilised in late winter / early Spring. The collected  sap (through tapping) is then heated to produce a concentrated syrup. Thanks to Montemari at Pixabay for image of gum arabic

Migrating hoverflies. Hoverflies are important pollinators, plus they also act as important predators  of crop pests such as Aphids.  Some hoverflies (like the pied and yellow clubbed hoverflies) spend the summer in the U.K. but then fly to the Mediterranean or North Africa come the autumn. They begin these migrations on sunny days but simply flying towards the sun would take them on a rather long winded  route.  A study by a research team at Exeter University suggests that they are able to account for the sun’s movement using their circadian rhythm - an internal clock.   If the circadian rhythm of the hoverfly is disrupted, then so is its flight path. Migrating cuckoos. Like many other birds, cuckoos are in decline.  Some time back, the BTO set up a research unit to learn more about the  decline and behaviour of cuckoos.  The work of this group has revealed details of the cuckoos’ migration routes and its winter homelands. Cuckoos have two routes out of the UK : They migrate out south west via Spain and Morocco - the WEST route, or  They take a south east route via Italy and the Balkans (the EAST route) but Both routes ultimately converge on the Congo Basin in Central Africa. However, the birds that take the WEST route leave some eight days later than those taken the EAST route, but were more likely to die en route. Most of the mortality of the birds occurs in the European section of the migration path.  This may be a reflection of the status of their stop-over sites.  Problems might include : Habitat change, droughts and wildfires Decline in food sources (e.g. large moth caterpillars). A lot more detail / information on this project can be found here. VOC’s The air around us is a mixture of different gases / particles / and aerosols.  An aerosol is itself a ‘mixture’ of very small particles (solid or liquid) in air.  These particles can come from a variety of sources :such as volcanoes, cars, trucks and wood fires. Examples of aerosols include  mist,  cigarette smoke,  fires volcanoes car exhaust fumes.   Some trees and plants also release volatile organic compounds (VOCs), for example  Pine trees release alpha-pinene.  Recent research has established that these volatile compounds / vapours are not only responsible for the characteristic scent, but are also important in the formation of aerosols found in the air in and around such woodlands and forests.   Atmospheric aerosols scatter and absorb light, and also influence the formation of clouds, though these processes are not fully understood.  Recent research by the University of East Finland has showed that biogenic aerosols (formed from VOCs) can reduce the amount of solar radiation that reaches the earth’ surface.  They help scatter the radiation back into space.  These biogenic aerosols increase the number of cloud droplets and make the clouds more reflective.