............................................. PLANTEA KINGDOM III. The Angiosperms

Introduction. The angiosperms are the plants with flowers and fruits, which means they are the most complex plants that exist. Thanks to that they are the ones with the most possibilities to survive. They already constitute 2/3 of all species of plants that exist. Theirs advantages over Gymnosperms are:

a) Generally the pollination is done by insects that go from flower to flower and this is a more efficient way than pollination by wind.

b) The fertilization and forming of seed happens much faster, and does not require a couple of years such as the pines.

c) The seed dispersal is more effective because they are inside the fruits. There are fruits that are eaten by animals which causes that seeds are being excretioned far from their progenitores, therefore far from their shadows which could make it more difficult for them to grow. Other fruits, such as coconut, float in the water and can overcross seas, other fruits have hooks to get tangled in the hair or feathers of animals, etc..

d) The germination of the seeds is much faster. For example, there are plants in high mountain that are born, reproduce and die leaving seeds for the next year, all this in just few weeks when there is no snow.

All of this makes the Angiosperms the most interesting group of all plants.

Activities to do. Read the explanations on the general characteristics and classification of plants and perform Multiple Choice Test 15.1 and Relate pictures with names 15.1. Then read the text on Angiospermes and perform Multiple Choice Test 15.2, Relate pictures with names 15.2 and Crossword 15.

1. The Angiosperms. They are the plants that have flowers and fruits, so they have theirs seeds enclosed in fruits. The flowers are formed by a series of modified leaves and they can distinguish the following parts:

1. Flower pedicel. It is the area that connects the flower to the stem. The flower pedicel ends floral receptacle which is an enlarging from where the other parts of flower sprout.

2. Calyx. It is the set of a small green leaves, called sepals, which are at the base of the flower.

3. Corolla. It is the set of leaves that usually have very bright or white colors, called petals. The vivid color is easily detectable by diurnal insects and white by nocturnal insects. Also, many times they emit smells to facilitate its detection and in its base secrete a sugary substance called nectar, such as the pollen, which provides food for many insects. This induces the visits of insects and therefore the transmission of pollen from one flower to another, meaning the insect pollination.

4. Androecium. It is the male part of the flower. It is formed by a set of filaments called stamens. In each stamen there can be distinguished one filament and two final enlargements called teaks. Inside the teak there are pollen sacs in which pollen grains are produced.

5. Gyneceum. It is the female part of the flower. It is formed by one or more structures in the shape of called long-necked bottle pistils. Each pistil is formed by one or more modified leaves that are called carpels. In a pestle can be distinguished three parts: the enlarged base or ovarian, neck or style and the mouth or stigma which have a plurality of hair that help setting pollen grains when they fall on them. Inside the ovary there are one or more formations called eggs, inside of which the female gametes or oospheres are located.

2. The biological cycle of the Angiospermes. The pollen grain that is attached to the stigma generates a long tube called a pollen tube that runs through the style up to an ovule. Through the fall the male gamete joins oosphere (fertilization) and forms a cell called a zygote. This, by multiplication, generates an embryo, and together with the rest, also transformed from the egg, constitutes the seed. While forming the seed, ovary walls fatten and transform into different layers of the fruit. If they are tender they are called fleshy fruits. For example apple, peach, grape, orange or melon. If walls are not fleshy, they are called dried fruits. For example, sunflower, wheat, acorn, pea and bean.

3. Types of the Angiospermes. There are two types, which are:

• The Monocotyledons. Are those that have seeds with one cotyledon.
• The Dicotyledons. Are those that have seeds with two cotyledons.

By the evolution, the monocotyledons are the most recent, but already have three times more species than the dicotyledons species. Its distinguishing features are: