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.
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.
The width of the annual ring is proportional to the quantity of manufactured food substances, and corresponds roughly to the amount of rainfall and warmth in a given year, i.e. in a favourable year it will be broad, whereas in an unfavourable year it will be narrow. A narrow ring is, therefore, an indication of the unfavourable influence Of dry weather and in trees sensitive to the cold of severe frosts, etc. This correlation today forms the basis of a new study known as dendrochronology.
By examining the rings in trees hundreds and thousands of years old scientists can determine long-lasting changes in the weather and pinpoint alternating periods of dry and wet years in times about which we have no meteorological data. In trees growing in tropical regions where growth is continuous throughout the year the annual rings are hot usually so clearly discernible. - 16035
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.
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.
The width of the annual ring is proportional to the quantity of manufactured food substances, and corresponds roughly to the amount of rainfall and warmth in a given year, i.e. in a favourable year it will be broad, whereas in an unfavourable year it will be narrow. A narrow ring is, therefore, an indication of the unfavourable influence Of dry weather and in trees sensitive to the cold of severe frosts, etc. This correlation today forms the basis of a new study known as dendrochronology.
By examining the rings in trees hundreds and thousands of years old scientists can determine long-lasting changes in the weather and pinpoint alternating periods of dry and wet years in times about which we have no meteorological data. In trees growing in tropical regions where growth is continuous throughout the year the annual rings are hot usually so clearly discernible. - 16035
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Where appropriate, a traditional style of garden planning can be used in your garden.
