Читать книгу Professional Make-Up - David Prescott - Страница 17

The leaves are the food factories of a tree. They take water supplied by the roots and carbon dioxide from the atmosphere and convert them to complex sugars, making use of sunlight to energize the reaction, in a process known as photosynthesis. The sunlight is captured by the green chlorophyll, which acts as a catalyst for the chemical reaction that takes place. Even red-leaved species feature green chlorophyll, but this may be masked by the red pigmentation which is present in greater abundance.

During the day, the leaves take in oxygen and carbon dioxide through pores, called stomata, which are usually found on the underside of each leaf. At night they expel carbon dioxide by respiration. The stomata are able to open and close in response to the ambient temperature and humidity, thus controlling the rate at which water evaporates from the leaf. Some water has to, of necessity, evaporate all the time in order that a fresh supply of moisture is kept flowing up towards the leaves from the roots.

Leaves vary tremendously between species. Large, flat leaves capture the maximum amount of light. Narrow pine needles are adapted to be drought resistant. They don’t get weighed down with heavy layers of snow, but have a large surface area in comparison with their volume. This way they are still able to capture plenty of light. Some species have waxy leaves in an attempt to prevent excessive evaporation, while others have leaves covered in dense hairs, which achieve the same end. All leaves have one thing in common: they emerge from buds which form at the tips of shoots (apical buds), often in clusters. On conifers, buds also form at random points along each shoot, of which the precise number and density depends upon the length of the shoot and the vigour of the tree. On broadleaved trees, a bud appears at the base of each leaf stalk (petiole). These buds are called axillary buds.

When pruning or pinching growing shoots on a bonsai, it’s important to consider the location of such buds because these are the points from which new shoots will emerge. If the bud faces left, then the shoot will grow to the left; if it faces right, the shoot will bear right.

Brightly coloured Trident Maple (Acer buergeranium) leaves in autumn. Chlorophyll is always green but its colour has been overwhelmed by red pigmentation.

The buds of three types of tree: (1) opening maple buds, (2) the buds of an elm, just opening and (3) pine candles extending as they mature.