Let us learn about Paleobotany. After reading this article you will learn about: 1. Concept of Paloebotany 2. Technique of Palaobotany 3. Important Strata 4. Work in India.
Concept of Paloebotany:
Palaeobotany or the study of fossil plants, i.e., the plants existed in the past and now are entirely extinct. This is the difficult branch of Botany in respect that the fossil plants are difficult to obtain and they are rather scarce. Whenever the fossil plants are found, they are in parts which are to be coordinated.
This is a tough process of the study. The fossils are cut in sections with a great difficulty and thereafter the preparations are made which require great labour, time and technique.
The study of fossils is useful academically as well as economically. The academic interest lies in that their study clears up to a great extent the inter-relationships and evolution of the ancient groups of the plants. The economic interest lies in that some fossils are confined to definite strata of earth crust and they are associated with petroleum, coal and similar other things of economic value.
Actually some coal fields were discovered only on account of the presence of certain fossils just above the coal mines. Another point of view of academic interest is that the fossils help in the determination of the climate of ancient time in different regions.
During Carboniferous period the earth was covered by very luxuriant forests and it is assumed that climate in those days was very uniform because the plants flourished in those times (i.e., Carboniferous period) were greatly the same on the whole surface of the earth.
According to one school of thought, the outer part of earth crust is solid and comparatively thinner than interior of earth which is supposed to be in molten condition. Some workers are of opposite view. They believe that the interior portion of the earth is firmer and more solid while the outer crust of the earth is of light matter.
They also presume that the interior crust of the earth consists of many heavy metals like iron and lead. Whatsoever might have been the position but it is very clear that the first crust which formed the first surface much have been very uniform.
Later on the water and air appeared and with the appearance of these two destructive factors the surface of the earth began to change. Rain and air affected the surface of the earth to great extent and at certain places the surface rose up in high mountains by bursting of interior of matter and at other places it sank down and formed seas and oceans.
The rocks withered off, the volcanic eruptions and other changes took place and the general topography of the earth was completely changed.
Rivers coming down from mountains bring down pieces of rocks and large quantity of sand when they flow in the plains. This sand settles down at the bottom of the water. Along with this sand the parts of the plants and animals which get into that sand would have a chance of being preserved. This preservation takes place in different forms.
The fossils are mainly found in the sand which has been brought down by the rivers from the mountains. This sand has become compressed and sedimentary rocks have been formed in the bottom of water. They contain the pieces of plants or entire bodies or bodies of animals which have been surrounded by mud and salt and they got the chance of being preserved.
This preservation takes in two forms:
These impressions may be of the surface markings of the plant material or be the markings of the internal cavities in the plant material. The surrounding mud gets deposited on the surface of the plant material or gets into the cavity and their impressions are left. In some fine fossils even details of the venation, structure of stomata and epidermal hairs have been studied.
In such impressions the plant material itself has decayed or turned into coal. However, the surface impressions cannot be relied upon as we know that the plants, e.g., Equisetum (a pteridophyte). Ephedra (a gymnosperm) and Casuarina (an angiosperm) gave same type of impressions, but all of them are widely differentiable and have no affinities and relationships with each other.
Another method of preservation of great importance is that the plant material when lying in water has become infiltrated with mineral matter such as lime, silica, magnesium salts and other similar substances.
These salts penetrate the minute cells and the organic matter is being replaced by mineral salts. The original organic matter may be completely or partially changed but its outline and general structure is left in the form of these infiltrated substances.
In coal mines generally the coal balls are found which are formed by the infiltration of calcium bicarbonate.
In another method of preservation in which rare and small parts of plant material such as seeds, pollen grains, spores, etc., have been preserved. In this method the plant material happens to fall in resin or amber extruded by some plants, such as pine trees and others.
Technique of Palaobotany:
The different methods of the study of fossil plants are as follows:
It is a laborious process and requires sufficiently great time. Usually the petrified specimens are cut in serial sections which give an idea of the actual structure of the fossil plant. These petrified pieces are cut into very fine slices by different methods. In one method each such piece is attached to glass plate and grounded to sufficient thinness and thereafter studied under the microscope.
Another improved method of the study of these petrified specimens is to prepare the films of the material by special techniques. The method of preparing thin films is as follows: First of all the surface of the section of the petrified material is made smooth. If the material consists of calcium carbonate, then on the smooth surface of the slice a film of 5 per cent hydrochloric acid is allowed to act for five minutes.
If the slice of the petrified material is silica then the film of 10 per cent hydrofluoric acid (HF) is allowed to act on the smooth surface for ten minutes so that the silica is dissolved.
The surface of the petrified section by the action of these acids becomes rough on account of the dissolution of the mineral matter. If any organic matter remains on this surface, now put hot gelatin on the surface. As soon as the things dry up, they are removed and studied under the microscope.
This process may be successful only in the case when organic matter is left in petrified specimens. In cases where organic matters are already decayed, such preparations are never good.
The fossils naturally would be pieces of plants. It is very rare that entire plant could have preserved. This way, only pieces can be studied. In such type of study the individual pieces are given botanical names, just as in living plants. The botanical names of the fossil plants are not so significant as those of living ones.
As they are represented by the pieces of the plants and, therefore, their generic names would be according to stem, leaf and root or any reproductive structure. The stems are usually given the generic names which end with ‘dendron’ (tree) or ‘xylon’ such as, Lygenodendron or Cladoxylon. The leaves end with ‘pteris’ or ‘phyllum’ and reproductive parts end with strobilus.
This way, the paleobotany is the study of the parts of fossil plants and in certain cases marvellous results have been obtained.
In the case of Lygenopteris, one of the Cycadofilicales of Carboniferous period which was found in pieces and later on the palaebotanists supported that all the pieces belonged to one particular plant. Later on after few years the complete intact plant was found.
Important Strata of Paleobotany:
The Palaeozoic and Mesozoic strata are very important from the study point of view of the fossil plants. It is in the upper middle Palaeozoic, i.e., the Devonian strata, we come across with the first land plants such as lycopods belonging to Lycopodiales, Equisetales, the seeded ferns, the primitive gymnosperms, the pteridophytes, etc. In the late Palaeozoic, i.e., both in the upper and lower.
Carboniferous strata the earth was covered up by the very luxuriant forests. These forests were formed by lycopods, horsetails, seeded ferns and later on with primitive gymnosperms.
The Carboniferous strata is most important. The coal mines are situated in this strata. The coal mines are the result of dense forests having got submerged in those times. The Mesozoic is also very important from the point of view that the first angiosperms made their appearance; otherwise the higher gymnosperms formed luxuriant forests in those times. In the later Mesozoic some of the gymnosperms disappeared.
Majority of the Cycads disappeared and only a few forms have been left up to the present day.
In India the most important strata is described technically the ‘Gondwana system’ named after Gondwana Kingdom. For the first time the rocks of this period were discovered near Narmada river.
Work on Paleobotany in India:
The first most work on Indian fossils was done by Fiestmental, the Director of Geological Survey of India. He published a monograph of Indian fossil forms. Thereafter Seward and Bencroft made a number of additions. From 1895 to 1909 most of the work on Indian fossils was carried on in Europe. It had been since 1919 till the death of Dr. Birbal Sahni, i.e. 1949, that work of Indian fossils had been added to a great of deal.
He first revised the known Indian fossils and then published a number of monographs describing numerous fossil forms. The most important Indian fossil of Cycads is Williamsonia sewardiana. In India it is only in few places that there is a good collection of fossil plants, e.g. Museum of Calcutta, the Lucknow University Museum; Presidency College, Madras, Prince of Wales College, Jammu.
The collections are made from Raniganj coal field, in Bengal, places near about Nagpur, Reeva state, Kotah state, in some parts of Kashmir near about the Sutlej river, salt range in Punjab (now in Pakistan), and Rajmahal hills, Bihar.