A plant fossil is any preserved part of a plant that has died long back. Fossils may be a prehistoric impression that may be hundred to millions of years old. Majority of the plant fossils are disarticulated parts of plants, it is rare to find plants to be preserved as whole.

Paleobotany is derived from Greek words paleon that means "old" and botany the study of plants. It is the branch of Paleontology that deals with recovery and identification or plant remains of geological past.

The reappearance of ancestral characters in some individuals is called atavism. Presence of rudimentary tail in new born babies, presence of thick hair on the Human body are examples of atavism.

It was speculated by Louis Pasteur (1862) that life originates from pre-existing life. He showed that pre-sterilised flasks kept closed airtight, with killed yeast, did not give rise to any life form, while in another flask kept open to air, living organisms arose from killed yeast.

Palaeontology.

Archaeopteryx.

Use and disuse theory
(i) Lamarck's Use and Disuse theory states that if an organ is used constantly, the organ develops well and gets strengthened.
(ii) When an organ is not used for a long time, it gradually degenerates.
(iii) The ancestors of Giraffe were provided with short neck and short forelimbs.
(iv) Due to shortage of grass, they were forced to feed on leaves from trees. The continuous stretching of their neck and forelimbs resulted in the development of long neck and long forelimbs which is an example for constant use of an organ.
(v) The degenerated wing of Kiwi is an example for organ of disuse.

(i) The age of fossils is determined by radioactive elements present in it.
(ii) They may be carbon, uranium, lead or potassium.
(iii) It is used in paleobotany and anthropology for determining the age of human fossils and manuscripts.

(i) Ethnobotany is the study of a region's plants and their practical uses through the traditional knowledge of the local culture of people.
Importance of Ethnobotany :
(i) It provides traditional uses of plant.
(ii) It gives information about certain unknown and known useful plants.
(iii) The ethnomedicinal data will serve as a useful source of information for the chemists, pharmacologists and practitioners of herbal medicine.
(iv) Tribal communities utilize ethnomedicinal plant and prepare medicine to cure many  diseases.

(i) Archaeopteryx is considered to be a connecting link between reptiles and birds.
(ii) It had wings with feathers like a bird. It has long tail, clawed digits and conical teeth like a reptile.

(i) 2 million years ago tree trunks that got buried along the river, incourse of time the organic matter was replaced by silica and was fossilized.
(ii) They retained their colour, shape and texture and was converted into solid rocks.
(iii) The annular rings, the texture, colours of the layers, nodes and every properties of plants are still visible.

Natural selection is a driving force for evolution.
Over production:
(i) Living beings have the ability to reproduce more individuals and form their own progeny. 
(ii) They have the capacity to multiply in a geometrical manner.
(iii) This will increase reproductive potential leading to over production.
Struggle for existence:
(i) Due to over production, a geometric ratio of increase in population occurs.
(ii) The space to live and food available for the organisms remain same
(iii) This creates an intense competition among the organisms for food and space leading to struggle.
The struggle for existence are of three types:
(i) Intraspecific struggle: Competition among the individuals of same species.
(ii) Interspecific struggle: Competition between the organisms of different species living together.
(iii) Environmental struggle: Natural conditions like extreme heat or cold, drought and floods can affect the existence of organisms.
Variations:
(i) The occurrence of variation is a characteristic feature of all plants and animals.
(ii) Small variations are important for evolution.
(iii) According to Darwin favourable variations are useful to the organism and unfavourable variations are harmful or useless to the organism.
Survival of the fittest or Natural selection:
(i) During the struggle for existence, the organisms which can overcome the challenging situation, survive and adapt to the surrounding environment.
(ii) Organisms which are unable to face the challenges, are unfit to survive and disappear.
(iii) The process of selection of organisms with favourable variation is called as natural selection.
Origin of species
(i) According to Darwin, new species originates by the gradual accumulation of favourable variations for a number of generations.