The leaves of plants are very important. They are the plant's manufacturing organs and act also in the capacity of lungs and partly as an excretory system. The most important plant function takes place in the leaves. Called photosynthesis, it is a process whereby the chlorophyll in the leaf cells with the aid of the sun's energy transforms atmospheric carbon dioxide into organic substances essential to plant growth.
A good identifying feature of some shrubs is their arcuate venation (cornelian cherry, dogwood, common buckthorn), where the secondary veins run parallel to the leaf margin towards the tip of the leaf. Leaf apices likewise differ in shape; they may be acuminate or acute (with long, slender, or short points), rounded, truncate (blunt) or emarginate (cleft). Leaf bases may be rounded (European green alder, wayfaring tree), cuneate, i.e. wedge- shaped, (barberry, mezercon) or cordate (hazel).
Leaves may be either simple, with a single blade, which may be lobed, e.g. the hazel, gooseberry and hawthorn, or compound, with three or more blades attached to one stalk, e.g. the bladdernut and common elder.
This is caused by the decomposition of the green chlorophyll, the predominance of yellow xanthophyll and red carotenoid pigments and increased level of anthocyanin in the cell plasm. Autumn coloration is likewise a distinguishing feature in a number of shrubs.
Thus, for instance, the leaves of Comes mas, Euonymus europaeus, Rhus typhina and Berberis thunbergi turn purplish-red, those of Forsythia suspensa dark violet, Viburnum opulus scarlet, Amelanchier oxalis orange, Rhamnus frangula and Corylus avellana yellow, etc. These autumn hues make just as lovely a picture in parks and in the wild as do the pastel tints of flowering shrubs in spring. Later a corky layer forms between the stalk and the twig, severing the vascular bundles nourishing the leaf.
These are microscopic openings in the epidermis of the leaf, located, as a rule, on the underside. They can be expanded or contracted to control the evaporation of water, depending on whether there is an overabundance or lack of this vital substance. Water is transported to the leaves via a vein-like system of vascular bundles that pass through the leaf stalk and branch in the leaf.
A good identifying feature of some shrubs is their arcuate venation (cornelian cherry, dogwood, common buckthorn), where the secondary veins run parallel to the leaf margin towards the tip of the leaf. Leaf apices likewise differ in shape; they may be acuminate or acute (with long, slender, or short points), rounded, truncate (blunt) or emarginate (cleft). Leaf bases may be rounded (European green alder, wayfaring tree), cuneate, i.e. wedge- shaped, (barberry, mezercon) or cordate (hazel).
Leaves may be either simple, with a single blade, which may be lobed, e.g. the hazel, gooseberry and hawthorn, or compound, with three or more blades attached to one stalk, e.g. the bladdernut and common elder.
This is caused by the decomposition of the green chlorophyll, the predominance of yellow xanthophyll and red carotenoid pigments and increased level of anthocyanin in the cell plasm. Autumn coloration is likewise a distinguishing feature in a number of shrubs.
Thus, for instance, the leaves of Comes mas, Euonymus europaeus, Rhus typhina and Berberis thunbergi turn purplish-red, those of Forsythia suspensa dark violet, Viburnum opulus scarlet, Amelanchier oxalis orange, Rhamnus frangula and Corylus avellana yellow, etc. These autumn hues make just as lovely a picture in parks and in the wild as do the pastel tints of flowering shrubs in spring. Later a corky layer forms between the stalk and the twig, severing the vascular bundles nourishing the leaf.
These are microscopic openings in the epidermis of the leaf, located, as a rule, on the underside. They can be expanded or contracted to control the evaporation of water, depending on whether there is an overabundance or lack of this vital substance. Water is transported to the leaves via a vein-like system of vascular bundles that pass through the leaf stalk and branch in the leaf.
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