Prema Iswary

In the life cycle of Pteridophytes, two distinct individuals can be observed i.e., there is a typical heteromorphic alternation of sporophytic and gametophytic generations. These two generations alternate with each other in regular succession one after the other, i.e. from sporophyte to gametophyte and from gametophyte to sporophyte. The sporophytic or asexual generation is diploid (2n) , while the gametophytic or sexual generation is haploid (n) . The actual phenomenon responsible for bringing about alternation in generation is the “ Periodic Reduction of Chromosomes ” as a result of meiosis . Due to meiosis a reduction in the chromosome number takes place which leads to the formation of haploid individuals . The haploid individuals in turn by produce haploid gametes which proceed the process of fertilization to produce diploid individuals . 1. Gametophytic Generation:-  The haploid individual bears sex organs, antheridia and archegonia . Antheridia produce male gamete i.e

Heterospory is the condition that interprets the production of spores of two different sizes and two different development patterns. The two different sizes are smaller spores also known as microspores and the larger spores also known as megaspores . Hetrrospory can be observed in some of the pteridophytes such as Selaginella, Marsilea , etc. They have differential developmental patterns because the microspores germinate to produce male gametophytes or microgametophytes that bear male sex organs called antheridia , and the megaspores germinate to produce female gametophytes or megagametophytes that bear female sex organs called archegonia. The two kinds of spores are produced in two kinds of sporangia. The microspores are produced in microsporangia and the megaspores in megasporangia . The microspores are produced in large numbers and are comparatively smaller than megasporengia which are produced in lesser numbers and larger in size. Importance of Heterospory (a) Th

A. CLASSIFICATION: Division – Pterophyta     Class – Leptosporangiopsida (Pteropsida)         Order – Marsileales             Family – Marsileaceae                 Genus – Marsilea The genus Marsilea comprises about 58 living species. The genus is worldwide in distribution and is very common in warmer parts of the world. The species of Marsilea are aquatic or amphibious plants – they grow either completely sub-merged in water, or partly or wholly out of water with their roots embedded in the muddy soil. In India, only 9 living species are found to occur. The common Indian species are – M. quadrifolia , M. aegyptica , M. coromandelica , M. brachypus , M. condenseta , etc. B. STRUCTURE OF THE SPOROPHYTE: 1. External structure:- The sporophyte, i.e., the plant body is well differentiated into – stem, leaves and roots. Stem – Stem consists of an elongated stolon-like rhizome with distinct nodes and internodes. Rhizome grows either on the surface of the soil or s

A. CLASSIFICATION: Division – Sphenophyta     Class – Sphenopsida        Order – Equisitales            Family – Equisitaceae               Genus – Equisetum Equisetum commonly known as horsetails comprises about 25 species and is world-wide in distribution. Equisetum can grow in wide variety of habitats. Some species grow in damp and shaded places, others grow in ponds and marshes or in sandy soil, near the banks of rivers, etc. Some others are found to grow in exposed dry habitats, along the road side and railway embankments. Some of the common Indian species of Equisetum are – Equisetum debile , E. arvense , E. Diffusum , E. elongatum , etc. B. STRUCTURE OF THE SPOROPHYTE: 1. External structure:- The sporophyte, i.e., the plant body is well differentiated into – stem, leaves and roots – Stem – The stem is underground, horizontal and much branched, which often penetrates more than a meter into the soil. The rhoizome is jointed and provided with nodes and

A. CLASSIFICATION: Division – Lycophyta      Class – Lycopsida          Order – Selaginellales              Family – Selaginellaceae                  Genus – Selaginella The genus Selaginella is commonly known as “ Club-moss ” or “ Spike-moss ”. Selaginella is a large genus comprising about 700 species and is world-wide in distribution. Some species of Selaginella are found to grow in temperate regions but majority of them are found to occur in the rain forests of tropical countries. The species of Selaginella is found to grow on the ground, on damp, shaded and humid conditions. Some species are also occurs in arid regions of the world. Temperate species are found to grow on damp shaded sides of the hills. About 55 species are found to occur in India. Of these the common species are S. rupestris, S. chrysocaulos, S. pallidissima, S. jacquemonth, S. megaphylla, S. pentagona , etc. B. STRUCTURE OF THE SPOROPHYTE: 1. External structure:- The sporophyte, i.e., t