Stream Corner

The shape and the structure of the leaves of conifers, called needles, are different. They are narrow, elongate and either rhomboid, semi-circular or elliptical in cross-section in order to limit transpiration as much as possible.

In most woody plants the leaf venation is netted, with a single primary vein and several secondary veins branching off at intervals.

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.

Most European broad-leaved trees are deciduous, in other words, they shed their leaves in the autumn. Only in southern, and in temperate parts of western Europe do some trees retain their leaves throughout the winter, e.g. the common holly, the laurel and the box. In the autumn the organic substances produced by the leaves are concentrated in the body of the tree and the leaves begin to change colour as a result of the decomposition of the chlorophyll and growing predominance of the red and yellow carotenoid pigments, along with the increase of anthocyanin in the cellular sap.

This autumnal coloration is characteristic of many species of trees, e.g. the leaves of poplar, birch and common ash turn yellow, the beech turns orange-brown, the red oak and wild service tree turn dull red and the staghorn sumach red or yellow-red. A corky layer forms between the leaf stalk and the twig, severing the connecting tissues.

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.