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Text A
The Flower
All seed plants are alike in that they all produce flowers. The flower is the part of the plant which is formed for seed production. A seed is always preceded by a flower. The seeds are the means by which most plants reproduce and in addition they are sources of food for man and feed for livestock. Consequently, it is highly important that the flower develop and function properly so asto assure a good yield of seeds. If you want to understand how plants produce seeds, it is necessary that you be familiar with the parts of the flower and the role of each in the reproduction process.
Parts of flower. A complete flower is made up of four principal parts, namely a) sepals, b) petals, c) stamens and d) a pistil. The number and position of the floral parts vary in different species and it frequently happens that one or more of them is missing, in which case the flower is said to be incomplete.
The flowers of the small grain lack both petals andsepals, and thus they are incomplete.
Neither sepals nor petals are directly involved in seed production. The former comprise the outermost part of the flower, protecting and supporting the other parts. They are usually green and leaf-like. Sometimes, however, they are brightly colored rather than green but it is not true for common cereals.The petals are located immediately to the inside of the sepals and unlikethe latter they are generally bright-colored but it is not true for grasses, including the common cereals. When taken together the petals are referred to as the corolla. The two remaining parts of the flower, namely, the stamens and the pistil, form the reproductive organs of the flower and are both absolutely essential for reproduction and seed production. It is in the stamens that the pollen grains which are necessary for fertilization are produced. The pistil should be looked for in the center of the flower. It consists of the style bearing on its top the stigma and a swollen base which is referred to as ovary. Within the ovary there are the egg-cells.
Pollination and Fertilization. For fertilization to occur the egg- cells must be fertilized by the pollen grains. The transfer of pollen from the stamens to the stigma of the pistil is spoken of as pollination. In self- pollinated flowers pollination results fromclose proximity of stamens and stigma. In some cases pollination occurs before the flower opens, as in most of the cereals and in some grasses; as a more general rule, however, flowers are pollinated from the flowers of other plants of the same species. Such plants are spoken of as cross- pollinated. Pollination is effected in some plants by wind while others have insect pollination. After the pollen has been transferred to the stigma some further processes take place which result inthe fertilization of the egg- cells. The latter then develop into seeds.
Notes:
inaddition– крометого, ктомуже, вдобавок
so as (to + Inf.) – длятого, чтобы
(to)beinvolved– участвовать в, быть связанным с
….but it is not true for common cereals – ноэтогонебываетуобычныхзлаковых
(to) be referred to as– называться; упоминатьсякак
Запомните!
(to) result -получаться в результате; произойти в результате
(to)resultfrom–происходить от; получаться из
(to)resultin-приводить к; давать в результате