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Q.
Circinate ptyxis (vernation) in ferns is defined as
NTA AbhyasNTA Abhyas 2020
Solution:
Pteridophyta, a diverse group of plants, have evolved more than Bryophyta in the following aspects:
1. Development of free-living sporophytic generation as the predominant phase.
2. Development of vascular tissue to conduct water and minerals from the soil.
3. Acquiring total terrestrial habitat.
4. In some species like Selaginella, development of two types of spores which later developed into seed habit in Gymnosperms and Angiosperms.
5. Reducing the gametophytic phase into a smaller, independent prothallus.
The rhizomatous stems of Pteridophytes have two types of leaves:
I. If there are large, green, photosynthetic leaves, they are called megaphyllous ferns. For example, Dryopteris. The leaves are pinnately compound. Individual leaflets are called pinnae.
II. If there are smaller in relation to the stem, they are called microphyllous ferns. For example, horsetails and Lycopodes. The leaves are small, lens-shaped, with a single mid-rib.
The young leaves vernation or the ptyxis is called circinate vernation, which means, the young leaves are coiled like watch-spring or dog-tail. The younger portion of the rhizome is covered with hairy ramenta. This is an unique character of ferns.