Lower plants

All the diversity of the surrounding plant world science divides into two sub-kingdoms: higher and lower plants. To the higher plants belong, the vegetative body of which is divided into organs, they have a stem, roots and leaves. In lower plants, on the contrary, there is no such division, in addition, there are no multicellular organs of reproduction. In modern biology, only algae are considered to be inferior plants, and a few tens of years ago, mushrooms and bacteria, as well as all organisms other than animals and higher plants, were also included in them.

For lower plants are characterized by: a variety of color, unicellular reproductive organs, aquatic habitat. Algae on our planet appeared first: the age of the fossil plants found in the layers of the Archean and Proterozoic era, amounts to about 3 billion years.

Some, guided by the name, think that the lower plants are primitive one-celled microscopic size. However, this is not quite true. Certainly, unicellular algae belong to this sub-kingdom, but it is also referred to as large, multicellular algae, the length of which reaches several tens of meters. Just like the higher ones, they can participate in the process of photosynthesis. Reproduction of algae occurs sexually and asexually (vegetatively or zoospores) by. All lower and higher plants contain chlorophyll, but the lower ones besides this pigment have others, which give them a specific coloration: brown, yellowish, red, etc.

Lower plants, examples

Algae can be divided into marine and freshwater (such a majority). Lower plants living in sea water can be located both on the surface and at depth. However, for life they need light, so at great depths - about 250-300 meters or more - they can not be met, because the sun's rays do not penetrate the water column.

The most famous sea kelp is laminaria or sea kale. It is a narrow leaf, reaching a length of several meters and clinging to the bottom of the processes-rhizoids. Laminaria is reproduced by zoospores - cells resembling a pear, containing a nucleus and chromatophores, equipped with flagella for movement. After exiting from the mother cell, the zoospora sorts out the flagella, moving in the water until it attaches itself to the nutrient substrate and gives life to the new alga.

Fucus is another species of marine brown algae. This multicellular plant looks like a bush, its length can reach two meters. Fucus is attached to the nutrient substrate by means of the soles, often forming whole thickets in the coastal waters. It reproduces sexually: in some mother cells, called antheridia and located at the edges of the plant, spermatozoa are formed, in other cells - oogonia - egg cells are formed. Under the influence of attractants - substances that attract spermatozoa to the eggs in the water, their fusion takes place and a zygote is formed, from which a new alga will subsequently grow.

In fresh water bodies, too, there are lower plants (algae). The most common of these is spirogyra. Spirogiru is easiest to meet in ponds with standing water: a bright green tint forms clusters resembling slimy cotton wool. If you look at it under a microscope, you can see a tall plant, consisting of large (up to 0.01 mm in length) cylindrical cells stretched in a row. Spirogyra can reproduce in two ways: sexual and vegetative. Unlike the fukus, in which the formation of the zygote occurs when the ovum and spermatozoids merge, in this alga, the zygote is formed by the fusion of 2 cells. Vegetative reproduction occurs when the filaments break, in this case a new plant is formed from each part.