The group of gymnospermous plants is characterized by existence of semyazachatok. In the subsequent there is a development of a seed, without formation at the same time of fruits and flowers. These are the main signs of gymnospermous plants.
Instruction
1. The most primitive and ancient representatives of group of gymnospermous plants were formed from one of species of ferns in the late Devonian Period. Today the few representatives of this group remained. It should be noted that many of them are included in the Red List.
2. The department of gymnospermous plants includes 4 main classes: cycad family, gnetovy, ginkgovy, coniferous. About 800 modern types belong to this group. The class of coniferous plants makes the prevailing majority (more than 500). They appeared on our planet at the end of the carbonic period. The class coniferous on all continents grows.
3. The most part of gymnospermous plants is evergreen, rare representatives treat bushes or listopadny trees, some represent ordinary lianas.
4. Plants of group of gymnospermous have leaves of a various form: from needle, scale-like to plumose, two-bladed, branched. Also the structure of seeds at this group is similar. At these plants of a semyapochka (semyazachatka) which consist of a protective cover and a megasporangium. They are located openly on inside of scale-like leaves. At coniferous these leaves form a cone and represent similarity of a spiral. It turns out that seeds of gymnospermous plants as though naked, without ovary.
5. The value of group of gymnospermous plants in the nature is very high. They enrich air with oxygen, forming the huge areas of the mixed and coniferous forests. It is necessary to remember that the woods fix sandy soils, weaken force and noise of winds, regulate water level in the rivers and the speed of thawing of snow. This dwelling of a large number of animals who eat generally cones of coniferous plants, seeds and escapes.
6. For people the gymnospermous coniferous plants bear practical value. Make the paper of wood, apply as wood product from which further make bridges, columns, cross ties, furniture, etc. About one today, wood of coniferous plants is used as fuel.
7. Coniferous trees of group of gymnospermous mark out huge amount of phytoncides in air. These are certain volatiles which suppress development of a set of pathogenic organisms. For this reason near coniferous forests often place hospitals and sanatoria for people who have diseases of respiratory organs.