IN THE BEGINNING … there were green leaves !

What makes a leaf green? Chlorophyll, of course, but there are other colours hidden all year!

Chlorophyll is PACKAGED in chloroplasts each cell in each green leaf!  See them in this magnified image. The leaves are green because green light is NOT absorbed by the leaves SO GREEN IS THE ONLY COLOUR WE SEE. The rest of the light spectrum or rainbow of visible light, especially red, yellow, orange and blue are absorbed to help with photosynthesis.

Leaves are generally attached by a leaf stalk, called a petiole. The petiole, shown on our flag,  

supplies water and nutrients and carries the manufactured sugars  to the rest of the plant.

The petiole twists the leaf to capture the most sunlight. These are the round petioles seen on dogwood leaves.  Flat petioles on aspen trees allow leaves to flap in the breeze, hence “trembling aspen.”

A healthy leaf has a balance of two hormones,  one to keep the leaf attached and the other to cut it off from the plant stem. As a leaf ages, responds to climate  or is damaged, one hormone becomes dominant and the leaf prepares to cut itself off for “leaf fall”. The  process is aptly called “abscission”.

Deciduous trees in Canada prepare for “leaf fall “,  working to drop all of their leaves very quickly as cool nights begin. Evergreen leaves or needles are lost or damaged by insects etc. and after an average of two years needles are dropped all year long – hence “evergreen”

The first stage of leaf fall is the breakdown and reabsorption of leaf pigments. Chlorophyll, the green pigment disappears first, exposing the other pigments – yellow, orange, red, purple for you to see. Anthocyanin molecules, seen here in cauliflower, are very healthy to eat – check out the benefits! Dark blue or black grapes too! The yellows and oranges are carotinoid molecules, and yes, they are found carrots!

A  special layer of weak-walled cells forms between the petiole and the stem of the plant to prepare for the break and cut off the exchange of materials. But meanwhile, underneath these weak cells, these clever trees form cork cells then add waterproofing molecules to form the leaf scar- used for  tree identification. The leaf, now cut off from the stem, falls with the other pigments showing its autumn colours. PS. Abscission is also how fruit and flowers fall off.

After abscission has occurred, you can find the scar showing the conducting tube bundles.

Each species has its own leaf scar shape and pattern of  “dots” where the circulatory bundles transporting food or water can be seen-  much like cutting a stalk of celery and looking the ends of those specialized bundles of tubes. Find them on this leaf scar on a butternut twig from Purdue University. Easy to recognize because, to me, the leaf scar resembles a camel’s face!

Fun Activity #1 : Collect small perfect maple red leaves, white candles, paraffin wax, old phone book and small artist paintbrush. Dry the leaves between the pages, then dip in small container of hot,* be careful, liquid paraffin and use paint brush to attach to the candle. Make great Canadian gifts. The waxed leaves can also be sent in a letter! Great for international friends!

Fun Activity #2: Take a winter discovery walk with magnifying glass will help you see these unique identifying leaf scar shapes! The silhouette of the whole tree will help you identify the too as well as its branching patterns. Binoculars for bud details is yet another way to have some fun identifying your tree, then add your tree to, ACER’s new mobile app! To confirm your guess of tree, visit where 50 species have detailed information.

Enjoy both this Fall and later on check out ACER’s winter discovery walk!

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