§ 20. Mosses

Mosses are distributed mainly in well-moistened places and only occasionally in arid areas (during the dry period they are at rest and resume their vital activity when precipitation falls).

Unlike algae, mosses have a stem and leaves, with the exception of a number of species of primitive liver mosses, in which the body is represented by a thallus. Mosses do not have real roots, they are replaced by rhizoids, with which they strengthen themselves in the soil and absorb water.

Since the body of mosses is divided into stems and leaves, and they reproduce by spores, they are classified as higher spore plants.

There are hepatic and leafy mosses.

Those who have an aquarium at home are well aware of the floating plant that covers the surface of the water with a green carpet. This is one of the liver mosses - Riccia (Fig. 68). Its body consists of a forked branched thallus. In good light, Riccia grows rapidly, forming dense cushions on the surface of the water.

Rice. 68. Liver mosses

Floating Riccia does not have rhizoids, but when water bodies dry up, remaining on damp soil, it can form them. Various types of liver mosses are found in damp forests, swamps, and reservoirs.

Leafy mosses. One of the most famous leafy green mosses is cuckoo flax (Fig. 69), it can often be found in swampy or simply wet places. Its slender brownish stems are covered with small dark green leaves and look like miniature flax plants.

Rice. 69. Moss cuckoo flax

Cuckoo flax has male and female plants. At the tops of male plants are the reproductive organs, in which mobile sex cells (gametes) develop - spermatozoa (from the Greek words "sperm" - seed, "zoon" - a living being and "eidos" - species).

In female plants, the genital organs are located at the tops with the female reproductive cell (gamete) - the egg.

On female plants, boxes on long legs develop, covered with hairy pointed caps. They look like a sitting cuckoo. Hence the name of the moss - cuckoo flax. Spores develop in the boxes. Spilling out and germinating, they form new moss plants.

Kukushkin flax is a perennial plant. Covering the soil in damp places with a continuous carpet, it often crowds out other green mosses.

moss structure

1. Consider a moss plant. Determine the features of its external structure, find the stem and leaves.
2. Determine the shape, location, size and color of the leaves. Examine the leaf under a microscope and draw it.
3. Determine if the plant has a branched or unbranched stem.
4. Examine the tops of the stem, find male and female plants.
5. Examine the spore box. What is the importance of spores in the life of mosses?
6. Compare the structure of moss with that of algae. What are their similarities and differences?
7. Write down your answers to the questions.

The representative of white, or sphagnum, mosses is sphagnum.

Sphagnum is a plant with a strongly branching stem (Fig. 70). Unlike cuckoo flax and other green mosses, it does not have rhizoids. The stem and branches of most sphagnum species are covered with small light green leaves. Each leaf consists of one layer of cells. These two different types of cells, their differences are clearly visible under a microscope.

Rice. 70. Moss sphagnum

Narrow green cells containing chloroplasts are connected to each other and form a continuous network. Organic substances are formed in these cells, which come from the leaves to the stem.

Between the green cells are other, larger ones. Their cytoplasm is destroyed, only shells with holes are preserved, so these dead cells are transparent and can be filled with water or air. Up to 2/3 of the leaf surface consists of these cells. Thanks to this structure, sphagnum quickly absorbs and conducts water.

Outside, the stems are also covered with transparent dead cells. Dead cells of sphagnum leaves and stems are able to absorb water 20-25 times their mass, hold it for a long time, gradually giving it to living cells.

Usually sphagnum grows on raised bogs, covering the surface of the soil with a continuous carpet, but it can also grow under the forest canopy among cuckoo flax. Where sphagnum settled, the soils are waterlogged. On excessively moist soil, trees grow poorly, become oppressed, and sphagnum, on the contrary, grows into a lush carpet, and the forest gradually becomes swampy.

Sphagnum reproduces by spores, just like cuckoo flax and other mosses. At the ends of the upper branches, it forms small boxes in which spores ripen.

The value of mosses in nature and human life. Mosses, settling in meadows, in forests, cover the soil with a continuous carpet, making it difficult for air to enter. This leads to acidification and waterlogging of the soil.

Leaf-stemmed, especially sphagnum, mosses cover swamps with a continuous carpet and, dying, form peat, which is widely used by humans. Peat is used as a fuel, fertilizer and as a raw material for industry. Wood alcohol, carbolic acid, plastics, insulating tapes, resins and many other valuable materials are obtained from peat.

New concepts

Moss. Spore. Higher spore plant. Sperm. Egg

Questions

1. Why are mosses called higher spore plants?
2. What is the structure of cuckoo flax?
3. How is sphagnum different from cuckoo flax?
4. How is moss different from algae?
5. What is the importance of mosses in nature and human life?

Think

Why don't even the largest mosses reach sizes over 80 cm?

Quests for the curious

1. Examine the leaves of sphagnum moss under a microscope. Note the structural features of the two types of cells of which they are composed.
2. Place some Riccia in a jar of damp soil. Cover the jar with glass and place in a warm, bright place. Make sure the soil is constantly moist. Watch what happens with Riccia.

Do you know that...

• Stumps and roots of trees, leaves and pollen of plants that lived millennia ago are preserved in peat layers. They are not completely destroyed, since there is little oxygen in the peat layer, in addition, sphagnum secretes substances that prevent the development of bacteria. When draining and developing swamps, well-preserved old boats, the remains of animals and people who died in the swamp, are sometimes found in the thickness of peat.
• Sphagnum was widely used during the war years as a substitute for cotton wool due to its high moisture capacity and good bactericidal properties.