cone or strobilus. Example: Selaginella , Equisetum . • They may be homosporous ( produce one type of spores- Lycopodium ) or Heterosporous ( produce two types of spores - Selaginella) . Heterospory is the origin for seed habit.
• Development of sporangia may be eusporangiate (development of sporangium from group of initials) or leptosporangiate (development of sporangium from single initial). • Spore mother cells undergo meiosis and produce spores (n). • Spore germinates to produce haploid, multicellular green, cordate shaped independent gametophytes called prothallus. • Fragmentation, resting buds, root tubers and adventitious buds help in vegetative reproduction.
• Sexual reproduction is oogamous. Sex organs, namely antheridium and archegonium are produced on the prothallus. • Antheridium produces spirally coiled and multiflagellate antherozoids. • Archegonium is flask shaped with broad venter and elongated narrow neck.
The venter possesses egg or ovum and neck contain neck canal cells. • Water is essential for fertilization. After fertilization a diploid zygote is formed and undergoes mitotic division to form embryo. • Pteridophytes show apogamy and apospory.
Reimer ( ) proposed a classification for pteridophytes. In this classification, the pteridophytes are divided into five subdivisions. . Psilophytopsida .
Psilotopsida . Lycopsida . Sphenopsida . Pteropsida.
There are orders and families in the classification. The success and dominance of vascular plants is due to the development of • Extensive root system. • Efficient conducting tissues. • Cuticle to prevent desiccation.
• Stomata for effective gaseous exchange. . . Economic Importance The Economic importance of Pteridophyte is given in Table .
. Table . : Economic importance of Pteridophyte Pteridophyte Uses Rumohra adiantiformis (leather leaf fern) Cut flower arrangements. Marsilea Food Azolla Biofertilizer.
Dryopteris filix–mas Treatment for tapeworm. Pteris vittata Removal of heavy metals from soils - Bioremediation Pteridium sp. Leaves yield green dye. Equisetum sp.
Stems for scouring. Psilotum, Lycopodium, Selaginella, Angiopteris, Marattia Ornamental plants . . Types of Stele The term stele refers to the central cylinder of vascular tissues consisting of xylem, phloem, pericycle and sometimes medullary rays with pith (Figure .
). Ectophloic Siphonostele Actinostele Plectostele Amphiphloic Siphonostele Dictyostele Solenostele Eustele