Birbal Sahni Was Elected to the Royal Society in 1936, Named a New Group of Fossil Plants from the Rajmahal Hills in 1948, and Founded the Lucknow Institute That Now Bears His Name

Scientists at the Birbal Sahni Institute of Palaeosciences write that Birbal Sahni (1891 to 1949) was the first Indian to take up palaeobotanical investigation, the study of ancient plants from their fossils. The Royal Society, Britain’s national academy of sciences, records his election as a Fellow on 7 May 1936.

His 1948 paper named the Pentoxyleae, a group of fossil seed plants from the Rajmahal Hills in what is now Jharkhand. The Institute of Palaeobotany he started in Lucknow in 1946 is today the Birbal Sahni Institute of Palaeosciences, an autonomous body funded by the Department of Science and Technology.

A childhood near the Salt Range

Sahni was born on 14 November 1891 at Bhera, a town in Shahpur district that is now in Pakistan. The Institute’s biography page names his parents as Ruchi Ram Sahni and Ishwar Devi and calls him their third child. His father taught chemistry at Lahore. Bhera lies not far from the Salt Range, a line of hills known for its fossil-bearing rock, and a family memoir on the Institute’s website says the children were often taken on trips to Khewra, where the salt mine is. Plant-bearing rock formations there, the memoir adds, were ones whose age he later worked on.

The same memoir has a few scenes from his youth. In the summer of 1905, when he was 13, he led his elder sister and brother down a ravine at Murree to collect crabs, and they got home at night with bleeding feet. In the summer of 1911 he crossed the Machoi glacier near the Zoji La pass with his father and picked up red snow, a rare snow alga (a simple water plant). Part of the sample was examined by Albert Seward at Cambridge, the memoir says.

Cambridge, Seward and a London doctorate

Sahni graduated at Lahore in 1911, having learnt botany there from the bryologist (moss specialist) Shiv Ram Kashyap. BS Venkatachala and A Rajanikanth, two scientists of the Institute who wrote a centenary account of him in 1992, say his father wanted him to join the Civil Service and he chose botany anyway. He went to Emmanuel College, Cambridge, graduated in 1914 and joined the Botany School under Albert Charles Seward, whose laboratory was known for fossil plants. Jawaharlal Nehru was a contemporary of his at Cambridge, they add.

His first paper, in the journal New Phytologist in 1915, reported pollen of other species inside the ovules of Ginkgo. The botanist P Maheshwari writes that Sahni pointed out how a fossil showing the same mix-up would probably have been read as one species.

Work on Acmopyle, a rare conifer from New Caledonia, went into his London D.Sc. thesis in 1919 and appeared in the Philosophical Transactions of the Royal Society in 1920. In it he split the gymnosperms, the seed plants whose seeds are not enclosed in a fruit, into Phyllosperms, with seeds on leaves, and Stachyosperms, with seeds on a stem or similar axis. TG Halle writes that the distinction is reflected in the views of later workers.

When Sahni went home in 1919, Venkatachala and Rajanikanth write, Seward politely declined to study more fossil collections from India and hinted that the country now had its own palaeobotanist. The collections went to Sahni. The 1920 revision of the Indian Gondwana plants, written with Seward, was a landmark that marked the revival of palaeobotanical research in India, according to the geologist SR Narayana Rao.

Lucknow, from 1921

After short spells at Lahore and Banaras Hindu University, Sahni joined the University of Lucknow in 1921 as Professor of Botany, in a department that had just opened. He married Savitri Suri, who went with him on his scientific travels, and stayed 28 years. The Indian Botanical Society was founded in 1921 partly through his efforts, and he was its president in 1924, Maheshwari writes. In 1943 he became head of the new Geology Department.

His vacations went to the Himalaya. The family memoir lists a trek from Pathankot to Leh in 1920 with Kashyap. In 1925 he and his wife were marooned in snow at Chor Panjal on the way to Gulmarg. Narayana Rao adds that he went to fossil sites with his hammer, notebook and Leica camera.

Fellows of the Royal Society from India before him included Jagadish Chandra Bose, whose later work was on plants, CV Raman and Meghnad Saha. The Institute’s list of his honours adds the general presidency of the Indian Science Congress in 1940 and the presidency of the National Academy of Sciences, India, in 1937 to 1939 and 1943 to 1944. He was elected president of the International Botanical Congress at Stockholm for 1950 and died before he could preside, Venkatachala and Rajanikanth write.

The chert from Nipania

Geological Survey publications on the fossil plants of the Rajmahal Hills date from 1863. A review by BD Sharma and R Harsh says a piece of chert (a hard rock made of silica) that GB Hobson of the Survey had collected and given to Sahni held petrified leaves. In 1932 Sahni took his students to the hills to find where it came from. HS Rao and KM Gupta reached the spot, at Nipania, and the whole party collected chert there the next day.

That year Sahni also described Williamsonia sewardiana, a fossil reproductive structure from the Rajmahals, and suggested which stem and leaves belonged with it. The Institute’s 1992 account calls the result one of the few reconstructions of a whole plant built from fossil fragments, and places the plant in the Early Cretaceous, about 110 million years ago.

Two researchers studied the Nipania material. AR Rao worked on the leaves and BP Srivastava on the stems and cones. Srivastava died before submitting his thesis, and Sahni published his unfinished work with an obituary note in 1946.

In 1948 Sahni brought stems, leaves and seed cones from Nipania into one group, the Pentoxyleae, in a paper whose title calls them Jurassic gymnosperms. Sharma lists its features: the plants are preserved by minerals that filled the cells, the main stem is distinct from short shoots that carry the leaves, and the stems have several steles, or bundles of conducting tissue. The stem Pentoxylon sahnii carries his name. The leaf Nipaniophyllum raoi carries Rao’s. Vishnu-Mittre found the male cone, Sahnia nipaniensis, in 1953, and a 1985 paper by Bose, Pal and Harris in the Philosophical Transactions of the Royal Society, titled “The Pentoxylon plant”, described the whole plant in detail.

Sharma’s 2003 note lists reports of related leaves and cones from New Zealand and Australia and a 1998 report from Antarctica. He argues that these differ in form from the Rajmahal plants and challenges the Antarctic identification. Later papers use the name Pentoxylales for the group.

The two Institute accounts differ on the age. Narayana Rao says Sahni concluded the Rajmahal flora was Jurassic, with not one species typical of the Cretaceous. The 1992 account puts Williamsonia sewardiana in the Early Cretaceous.

A few weeks before his death, Narayana Rao writes, Sahni led an excursion to the Rajmahal Hills, where he greeted the discovery of Williamsonia-bearing beds near Amarjola with great joy.

Fossil plants as evidence for geologists

Narayana Rao describes a gap Sahni set out to close. After Ottokar Feistmantel finished his work on the Indian Gondwana flora in 1886, Indian geologists doubted that fossil plants could date rocks, following a caution WT Blanford had put in 1876. Sahni, in Narayana Rao’s judgment, did more than anyone else to persuade them otherwise. The preface to the Institute’s 1992 centenary conference volume carries a line from him as its motto: “Fossil plants represent the debt that Botany owes to Geology.”

His fossil work ranged over Queensland, New South Wales, New Caledonia, New Zealand and Burma as well as India, Venkatachala and Rajanikanth write, and they credit his plant evidence with helping the understanding of continental drift and the rise of the Himalaya. Glossopteris, a woody seed plant of the southern continents, shows how such evidence works: the Geological Society of London notes that its fossils turn up in Australia, South Africa, South America, India and Antarctica. Narayana Rao says Sahni took up a theory that continents once separated by oceans had drifted towards one another, a counterpart to Alfred Wegener’s picture of continents drifting apart.

Micropalaeontology, the study of microscopic fossils, was a second interest. Narayana Rao says Sahni extended the technique to the Tertiary rocks of Assam and to the measurement of geological time in India, and Venkatachala and Rajanikanth credit him with starting work on fossil leaf skins (cuticles) and on pollen and spores in India.

Two of his dating calls were disputed at the time. In 1934 he published the first of his studies of the silicified plants found between the lava flows of the Deccan Traps. Blanford and others had argued from the rocks for a Cretaceous age. Sahni found the flora “distinctly Eocene”, Narayana Rao writes. The Salt Range was the other. About four years before 1947, he wrote that year, he dissolved a little saline earth from the Khewra mine and looked at drops of the brine under a microscope, because the brine “ought to show at least some minute traces of organic remains”. He found shreds of the wood of flowering trees and conifers and the remains of winged insects, and argued that salt holding them could not be as old as the Cambrian. Dr Gee and other field geologists held that the salt lay in normal sequence below the Cambrian and was older still. “Palaeontology is a surer foundation for stratigraphy than field evidence,” Sahni replied. His 1945 paper with BS Trivedi in Nature set out the microfossil case.

Later work has moved the Deccan date. Narayana Rao wrote that the Eocene view had since won its strongest backing from geologists. Keller and colleagues reported in 2009 that the main Deccan eruptions took place from the late Maastrichtian to the early Paleocene, and found early Danian foraminifera (shelled microfossils) in intertrappean beds at Jhilmili in Chhindwara district, Madhya Pradesh. They place the boundary between the Cretaceous and the Tertiary inside those beds, which makes them older than the Eocene. That is one locality, but Sharma and Harsh list Mohgaon Kalan in the same district among the places Sahni studied. Berkeley News reported in 2019 that the impact at the end of the Cretaceous dates to 66,052,000 years ago, give or take 8,000, with the main Deccan eruptions within about 50,000 years of it.

The Salt Range question has not been closed. A 2021 preprint by Lachlan Richards and colleagues says the age of the Salt Range Formation is “poorly constrained”, bounded above by the early Cambrian Khewra Sandstone and below by older basement rock, while the INDPLEX lexicon lists it as Ediacaran. Richards and colleagues also describe the formation as the main sliding surface beneath the Himalayan fold-and-thrust belt, the kind of structure Sahni and Gee had argued over.

A hammer, a mound at Rohtak and 1945

Sahni’s interests reached into archaeology. In March 1936 he found coin moulds at Rohtak, a find the family memoir describes as an archaeological discovery made by a palaeobotanist with the stroke of a geologist’s hammer. He published a paper in Current Science in 1941 on Yaudheya coin moulds from Sunet, near Ludhiana. A monograph for the Numismatic Society followed in 1945, in which, the memoir says, he compared moulds from Indian sites with those from China. The memoir adds that a numismatist described the work as setting a new standard of research in the subject.

The institute, and the week after the foundation stone

Sahni had long wanted a research centre for fossil plants. Venkatachala and Rajanikanth write that he felt palaeozoology, the study of animal fossils, had a place in several university departments and the Geological Survey while plant fossils were neglected.

In September 1939 he convened a committee of palaeobotanists, and the Institute’s history page gives 19 May 1946 as the day eight of its members signed the memorandum for a Palaeobotanical Society. On 10 September 1946 the Society’s governing body set up the Institute of Palaeobotany and named him first director, in an honorary capacity. The Institute started in the Botany Department at Lucknow University. Its first assets included fossil collections and a library belonging to Sahni and a small fund given mainly by the Sahni couple and the Burmah Oil Company. In September 1948 it moved to a bungalow on 3.5 acres at 53 University Road, a gift of the government of the United Provinces.

Nehru laid the foundation stone for a new building on 3 April 1949. According to Venkatachala and Rajanikanth, Sahni told the gathering that the stone symbolised “the great fact of the antiquity of plant life on the globe”. He died on 10 April 1949, according to the Institute, a week after the ceremony. A page on Savitri Sahni puts his death at midnight between 9 and 10 April.

Savitri Sahni took on the task of finishing the Institute. The building was ready by the end of 1952, and Nehru dedicated it to science on 2 January 1953. In 1951 UNESCO included the Institute in its technical assistance programme, and Professor OA Høeg of the University of Oslo served as director from October 1951 to August 1953. She became president of the Institute in October 1959. On 9 July 1969 the Institute was registered as a separate body, and the Palaeobotanical Society handed it over in November that year. The President of India gave her the Padma Shri in 1969. She died in Lucknow on 26 April 1985, and the Institute says she left her estate to the nation to support research in palaeobotany.