All variety of the surrounding flora science divides into two subkingdoms: higher and lower plants.To include higher plants, vegetative body is divided into organs, they have a stem, roots and leaves.In lower plants, on the contrary, such a separation is not, moreover, no multicellular reproductive organs.In modern biology to lower plants include only the algae, and even a few decades ago to them also ranked as fungi and bacteria, as well as all organisms other than higher plants and animals.
for lower plants are characterized by: a variety of colors, single-celled reproductive organs, aquatic habitats.Algae on our planet came first: the age of fossil plants found in Archean and Proterozoic strata of age, has about 3 billion. Years.
Some, focusing on the title, people think that the lower plants - primitive single-celled microscopic size.However, this is not true.Of course, single-celled algae belong to this subkingdom, but it also applies to both large multicellular algae, the length of which amounts to several tens of meters.Just as higher, they can participate in the process of photosynthesis.The reproduction of algae occurs sexual and asexual (vegetative or zoospores) way.All the lower and higher plants contain chlorophyll, but lower pigment addition, there are other, which give them a specific color: brown, yellowish, red, etc.
Lower plants, examples
Algae can be divided into marine and freshwater (the majority).Lower plants living in the sea water, can be located on the surface and at depth.However, for life they need light, so at great depths - about 250-300 meters or more - they do not meet, as the sun's rays do not penetrate through the water column.
most famous sea kelp - kelp or seaweed.It is a narrow sheet, reaching a length of several meters, and clinging to the bottom spikes, rhizoids.Propagated kelp zoospores - cells, is shaped like a pear, containing the nucleus and chromatophores, equipped with flagella for movement.After leaving the mother cell zoospore iterates flagella, moving in the water as long as not attach to the substrate and nutrient not give birth to a new algae.
Bladder - another kind of sea kelp.This multicellular plants looks like a bush, the length can reach two meters.Fucus is attached to the nutrient substrate by means of the foot, often forming whole thickets in coastal waters.Propagated he sexually: in some maternal cells called antheridia and on the sides of the plant, formed sperm, other cells - oogonia - formed egg.Under the influence of attractants - substances that attract water sperm to the eggs, they coalesce and the zygote is formed, from which subsequently grow new algae.
In freshwater reservoirs also occur lower plants (algae).The most common of them - Spirogyra.Spirogyra easiest to find in reservoirs with standing water: bright green slime forming clusters resembling slimy wool.If you look at it under a microscope, you can see the plant thallus consisting of large (up to 0.01 mm) cylindrical cells extending in a row.Spirogyra can reproduce in two ways: sexual and vegetative.Unlike the fucus, in which the formation of the zygote occurs at the confluence of the egg and sperm cells, this seaweed zygote is formed at the confluence of 2 cells.Vegetative reproduction occurs when the strand breaks, in this case from every part of the new plant is formed.
