8.2.3 Importance or Advantages of Bryophytes Some of the uses of bryophytes are as under.
- They prevent soil erosion by holding soil in place.
- The rocks are broken down into soil by their physical and chemical action. They increase soil fertility as they decay into soil.
- They also provide food for herbivores.
- They retain soil moisture.
- Some bryophytes have medicinal value as well.
8.3 Seedless Vascular Plants
The seedless vascular plants are a subgroup of tracheophytes. The tracheophytes have vascular tissue, i.e., the xylem for the conduction of water and minerals. phloem for the conduction of organic food. All vascular plants have tracheids in their xylem and are thus called tracheophytes. They are successful land plants with dominant sporophyte and reduced gametophyte generation.
The tracheophytes can be subdivided into the following groups. Subdivision Psilopsida Subdivision Lycopsida Subdivision Sphenopsida (iv) Subdivision Pteropsida
8.3.1 Sub-division Psilopsida: (whisk ferns)
They are the earliest primitive seedless vascular plants. extinct, e.g., Rhynia, Cooksonia. There are only two living Tmesipteris. Psilopsida has the following characters.
These plants are rootless, leafless, and seedless. Most of them have been the rhizome is horizontally placed and being genera Psilotum and Underground stem, the rhizome is present to anchor the plant body. minerals. rhizoids for absorption of water and the Aerial stem is green, photosynthetic, and has forked branches.
The reproductive organs are sporangia which are borne on the tip of branch and contain spores. Stem Sporangium
8.3.2 Lycopsida (Club mosses)
It includes plants like Lycopodium and Selaginella. These plants are also called club mosses or spike mosses due to their club/spike-shaped cones or strobilli and small moss-like leaves. These plants have the following characteristics.
The plant body is sporophyte which is differentiated into roots, stems, and leaves. Their leaves are called microphylls.
Leaves may be spirally arranged or opposite. Sporangia develop singly on the upper side of the leaf such a leaf is called sporophyll. Sporophylls may be grouped together to form a cone or strobilus. These plants may be homosporous (Lycopodium) or heterosporus (Selaginella). Gametophyte of lycopsida is underground and has a fungal association called mycorrhiza.
8.3.3 Sphenopsida (Horsetail)
The plants of this group are called arthrophytes because the whole plant consists of a large number of joints. These plants are found in humus and wet places around the world. There is only one surviving genus Equisetum. They have the following characteristics.
The plant body is sporophyte differentiated into roots, stems, and leaves. Leaves may be broad or scale-like and are always arranged in whorls. The main stem is jointed and has ridges and furrows. From each node, there are given whorls of branches. The sporangia develop on sporangiophore. The sporangiophores group together to form cones. The gametophyte is thalloid and grows on clay soil or mud. Stabilus
8.3.4 Pteropsida
The Pteropsida is a heterogeneous group of seedless vascular plants that consist of a sub-group or class Filicinae. These are found in moist and warm tropical areas. Rhizome detail
Class Filicinae:
This class includes ferns which are the largest group of seedless vascular plants. These plants possess the following important characteristics. These plants are usually found in moist and shady places. An important characteristic of this group is that sporangia are attached to the underside of leaves. Such leaves are called fronds.
The immature or young frond has a coiled pattern of development like watch spring and it is called circinate Vernation. Some ferns are epiphytes, i.c., that grow on the bark of trees. The plant body is differentiated into leaves, stems, and roots. Plants range in size from 1cm-24 m. Leaves are megaphyllous and may grow up to 5 meters (in a tree fern), Sex organs are antheridia and archegonia, for example: Adiantum, Pteris, etc.
Life cycle of Fern (Adiantum):
two different generations (sporophyte and gametonieris etc. Adiantum involves both asexual and sexual reproduction, i.e., morphologically
Sporophyte:
The plant body is diploid sporophyte bearing groups of sporangia or sori on the underside of margins of leaflets. Mature sori become black. The leaves bearing sporangia are called sporophylls. The sporangium is a flattened, biconvex capsule born on the multicellular stalk.
These capsules contain spores. Each spore is a simple cell consisting of cytoplasm and nucleus surrounded by two layers of cell wall. When the spores fall on suitable soil, it is germinate into a haploid gametophyte called prothallus.
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