Leaf Patterns Olson heads to his lab to study photos he took as he soared above the trees. From up there, he can see how tree branches and leaves are arranged. On some trees, the pattern looks like a head of broccoli. Some look like a brain. Te moringa’s leaves look like a green cloud of feathers. Tese patterns help each tree get as


much sunlight as possible. Take the African raffia palm. It grows the largest leaves in the world. One leaf may grow as long as 20 meters (65 feet). If these leaves grew close together, they’d block each other’s light. So instead, the palm’s leaves grow far apart. Each leaf gets lots of sun. Olson’s moringa tree has small leaves. So


the tree grows lots of leaves close together. Tey sprout from many skinny branches. Leaves have other ways to get light,


too. Some grow in a spiral around a plant’s stem. Other leaves have notched or cutout edges. Light can shine around them and onto the leaves growing below.


Keeping Their Leaves


Not all trees lose their leaves in winter. Most conifers keep their leaves year round. The leaves on these trees are hard and narrow. They look like needles. These needles may be thin, but they can gather sunlight. Like the leaves of other trees, they carry out photosynthesis.


Life and Death Tree leaves collect sunlight and make food all during spring and summer. Ten comes fall. Days shorten. Temperatures drop. Tese changes send a message to leafy deciduous trees. It’s time to shut down for the winter. Te shorter days means there’s less


sunlight. So photosynthesis slows way down. Te chlorophyll in the leaves starts to go away. Leaves turn red, yellow, and brown. Actually, these colors are always in the


leaves. Te strong green of the chlorophyll usually hides them. When that fades, the other colors get a chance to shine. Finally, all the leaves’ food is gone. Te


leaves die and driſt to the ground. Te trees use their stored glucose to survive until spring. Ten they grow new leaves.


Into the Air Early the next day, Olson again buckles himself into his paraglider. He wants to study the moringa trees in the early morning light. He revs the motor. Te propeller starts to


spin. Suddenly, he’s airborne. He soars over the trees. Birds fly under him. Above, the warm sun shines down on him and the leafy trees below. As Olson knows, those leaves are just beginning their day of hard work.


Wordwise


chlorophyll: a chemical in leaves that catches the sun’s energy


conifer: a tree that stays green year-round


deciduous tree: a tree that sheds its leaves at the end of a season


photosynthesis: the process by which organisms use sunlight to make food


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