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.
The primary vein divides the blade into two, generally equal, halves. In some woody plants, however, the halves are not identical, especially at the base, and these are termed asymmetric (elm, hackberry). In other species the leaf may have several veins branching out from the base (maples); such leaves are usually palmately lobed.
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 leaf then falls to the ground, giving back to the soil a substantial part of the minerals taken from it. The shedding of leaves is the result of the climate, in these latitudes, where in winter trees other than evergreens limit their life processes to the minimum, eliminating the water in their tissues in order to withstand better the harsh weather of the cold months.
In most woody plants the leaf venation is netted, with a single primary vein and several secondary veins branching off at intervals.
The primary vein divides the blade into two, generally equal, halves. In some woody plants, however, the halves are not identical, especially at the base, and these are termed asymmetric (elm, hackberry). In other species the leaf may have several veins branching out from the base (maples); such leaves are usually palmately lobed.
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 leaf then falls to the ground, giving back to the soil a substantial part of the minerals taken from it. The shedding of leaves is the result of the climate, in these latitudes, where in winter trees other than evergreens limit their life processes to the minimum, eliminating the water in their tissues in order to withstand better the harsh weather of the cold months.
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Where appropriate, a traditional style of garden planning can be used in your garden.
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