Gnetales is an order of the gymnospermic seed plants. This order is composed of three genera- Gnetum, Ephedra, and Welwitschia. Chamberlain (1935) has placed all three genera in a single-family Gnetaceae. But Markgraf (1951) has been split up the order…
Coniferales is a gymnospermic order like Ginkgoales. The members of this order form the common conifers. The order Coniferales includes both fossil and present-day living genera. The Coniferales reached their maximum development probably during the late Jurassic period or the…
Ginkgoales is a special gymnospermic order having one living genus (Ginkgo biloba). The members of this order once had an almost worldwide distribution in the Jurassic period. The fossil members of this order probably appeared in the Devonian period of…
Cycadales is a gymnospermic order. Members of this order are mostly inhabitants of tropical and subtropical regions. Cycadales include both living and fossil genera. They originated in the Mesozoic era and continued up to the Jurassic and Cretaceous periods. Only…
The Eukaryotic cell is the most advanced type of cell which is present in both animals and plants. Dougherty (1957) has divided cells into two types (based on the organization in the nucleus of the cell) – The Prokaryotic cell…
The mesokaryotic cell is the intermediate cell of the Prokaryotic cell and the Eukaryotic cell. Dodge has first used the term mesokaryotic in 1966 for the cell that contains an intermediate nucleus (both eukaryotic and prokaryotic characters are present). Although…
Viroids are the group of pathogens of some higher plants. Theodor Otto Diener introduced the viroid in 1971 for a new group of sub-viral plant pathogens. He was the first to discover the causal agent (Potato Spindle Tuber Viroid or…
In 1957 Dougherty has divided cells into two types based on the organization in the nucleus of the cell. One is a prokaryotic cell (primitive cell) and the other is a Eukaryotic cell (ideal cell). Prokaryotic cells are the most…
Phylum Echinodermata represents the most advanced invertebrate phylum closer to the chordates. They vary substantially in size which may range from 1 cm to about 2 m in length. In 1734 Jacob Klein has coined the name Echinodermata. The name…
Phylum Mollusca is the second largest invertebrate phylum containing more than 90000 described living species after phylum Arthropoda. Johnston has first coined the name Mollusca in 1650. Although Aristotle was probably the first person to recognize the mollusks. He divided…