About Leaves

About Leaves
by Jamie Rainbows

Let us now take a look at the structure of the tree trunk. In the centre, there is a narrow column of pith and around it a continuous shaft of wood, called the xylem. This is made up of concentric circles known as the annual rings. Then comes the thin layer of phloem and, on the outside, the bark, which in older trees may be split and furrowed.

This is an adaptation to the environment in which they grow, for they are trees of the north and of the mountains where the climate is harsh and the summer short. To make the best use of this brief period, and not to lose time producing new leaves, they generally retain their foliage throughout the winter.

To be able to bear the weight of the snow and survive frost and lack of water, the leaves have a different shape and structure. Most of their cells are thick- walled and their surface is often protected by a waxy layer.

The strip of compact summer wood is easily distinguished from the strip of the following year’s spring wood so that on a stump we can clearly see the yearly growth, in the form of annual rings, and thus easily determine the age of the felled tree.

The pine leaves live for a shorter time than those of the spruce; and leaves of a spruce growing at low elevations live longer than those growing in harsh conditions.

The process is slow and gradual, and the tree sappears unchanged. Only the amount of needles on the ground beneath i serves as an indication of its shedding rate.

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