Why do laurel and holly trees have shiny waxy leaves?

Laurel and holly - trees have developed special kinds of leaves to seal the water inside them during the winter months. Both trees are evergreen. Instead of dropping all their leaves in autumn, they shed old ones and grow new ones through out the year. In winter the soil is too cold for the trees to draw water from it through their roots. Normal leaves would continue to transpire and to give off moisture until the trees died of drought. But the special leaves of the holly and laurel hold the water. Their waxy surface and leathery texture make certain that the water is contained safety within the green tissues. Some of the holly leaves have a further modification. On the lower branches which are within reach of browsing animals, each leaf has a series of sharp points along its edge. The higher leaves have only a single point. The leaves of the cherry laurel, if crushed give out a faint but unmistakable smell of almonds because of the weak fumes of hydrocyanic (prussic) acid found in them. These fumes are poisonous. Scientists who want undamaged specimens of dead insects sometimes kill them by putting them with crushed laurel leaves in a closed glass tube.