How many angiosperms exist on earth?
Angiosperms - is the youngest, the most numerous and most owlrshennaya group of modern plants, which appeared in the middle of the Mesozoic era, and quickly became the dominant group of plants around the globe. The number of species of angiosperms have not yet fully elucidated, the figure is about 200-250 species. Most of these plants can be found on the website free eniklopedii - .
The most characteristic feature of angiosperms is the presence of flowers, fruits and seeds. Unlike the gymnosperms, angiosperms rudiments of seeds contained in the ovary, which is part of the pistil, the latter was formed as a result ofGrowth edges of one or more carpels, which are modified apical leaves, which grow together to form a pistil.
Another feature is the presence of an eight angiosperm embryo sac, in which the double fertilization - a process that is not repeated in any of the other departments of the Republic of Armeniastitelnogo world. The sexual generation (gametophyte) angiosperms underwent a further reduction compared to the gymnosperms. Male gametophyte is represented by 3 cells, 2 of which are gametes. Female gametophyte is represented by 8-core embryonic sack. Most angiosperms are pollinated by insects (entomophily), second (anemofiliya), water (hydrophilic) or birds (ornithophily). Unlike other parts of the plant world angiosperms are present in the wood vessels (the trachea). For angiosperms characterized by an extraordinary variety of shapes and sizes of leaves. Angiosperms - it is one, two and perennial herbaceous plants, as well as trees, shrubs and bushes.
From chega flower is?
A typical flower of angiosperms has peduncle, receptacle, cup, whisk, androecium and gynoecium is modified escape. The stem of the flower is represented receptacle and peduncle (if it does not, a flower called sedentary). Pedicel often bears bracts. Flowersetolozhe in different plants have different shapes: flat, concave, conical, expansion and so on. n. On the receptacle are all the parts of a flower. The set of sepals is called the calyx, it is protective. Calyx usually formed from a range of sepals, but some plants form the outer circle of the second sheetglasses, called epicalyx.
The set of petals is called the corolla, which consists of three or more colored leaves which attract insects for pollination. Corolla is sympetalous, right or wrong. Whisk together form a cup and covers the flower, or perianth. Perianthcan be double if the flower has a calyx and corolla.
What is the androecium?
androecium is the set of stamens. Stamen consists of filaments and anther. Stamens in the flower may be two or more. The number of stamens is an important feature in the systematic classification of plants. StaminateSingle strand carries pylyak, which consists of two halves connected vyazaltsem. Each half 2 carries pollen bags where the developing pollen.
On the cross-section dusting has the anatomical structure. Above it is covered with the epidermis, which houses the so-called fibrous layer, which consists of large cellswith thick walls contribute to break the wall of the boot.
Formation of flora and fauna on Earth
Scientists believe that the Earth was formed about 4.5 billion years ago and...
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