Even a cursory glance at Birbal Sahni's work on fossil plants inevitably conveys a vivid impression of its extraordinary compass and variety. His researches, in fact, ranged over practically the whole field of palaeobotany. He not only selected the concrete objects of his investigations from all major groups of vascular plants and from nearly all plant-bearing geological systems; but in dealing with this diverse material, and in his more general discussions, he approached the problems involved from every possible angle. Thus his work on fossil plants resulted in contributions to, all pertinent branches of botany, as well as to stratigraphy, palaeogeography and other related lines of geological research. One has the impression that he felt on quite familiar ground whether he was studying intricate anatomical structures, analyzing taxonomic relationships, describing fossil floras, or discussing their bearings on problems of climatic changes or supposed displacements of continents. The reasons for the comprehensive character of Sahni's work may not be evident to botanists insufficiently acquainted with the study of fossil plants and may, therefore, warrant an attempt at analysis.

It is by no means unusual in fossil botany to find that the publications of one author deal with many matters that are little related except that they concern plants of the past. The palaeobotanist is rarely free to choose his subjects solely with a view to pursuing connected inquiries into certain problems. As a rule he is dependent on the material at his disposal; indeed, most work on fossil plants has been occasioned by access to this or that collection. Fossil plants are scarce, the material is precious and its examination may not infrequently appear to be a duty. It is in fact a characteristic feature of the history of palaeobotany that even the most important advances have often been made by studying and describing accidentally discovered or acquired material. Kidston and Lang, for instance, did not set out to inquire into problems of general morphology. Their primary task was to examine, analyses and describe the structures of the petrified plant- remains from the Devonian of Rhynie; but their work, nevertheless, profoundly influenced our conception of certain fundamental problems connected with the morphology of vascular plants. No doubt the claims of the material often had a particular significance in Sahni's case. His country is rich in fossil plants, and important un described collections as well as imperfectly explored plant-bearing deposits awaited his attention when, at first quite alone, he began work in this vast field. No doubt he was often inspired by a sense of duty not only to botanical science but also to the needs of Indian geology.

At the same time Sahni's researches largely group themselves along certain lines of connected study, which he evidently chose in preference to others because of their bearings on questions of general importance. A very considerable part of his work was also concerned with the analysis and survey of problems which could be studied without direct reference to concrete material. On the whole it would appear that the diversity of his researches was largely an expression of the wide range of his interests, his extensive knowledge and intellectual versatility. Some of the characteristic features of his many- sided scientific personality became apparent at a remarkably early stage of his career as a research worker.

There can scarcely be any doubt that Sahni was first attracted to palaeobotany through the influence of the late Professor Sir A. C. Seward, his teacher at Cambridge. After graduating in 1914, he began research at the Botany School where, under Seward's leadership, studies of living and extinct plants were combined to an extent at that time unparalleled elsewhere. At first Sahni engaged in morphological and anatomical investigations of recent plants, chiefly pteridophytes and conifers. Before long he also took up palaeobotanical work, while continuing his studies of living plants. For the remainder of his stay at Cambridge, till he returned to India in 1919, he divided his time between these branches of research, doing a surprising amount of excellent work in both.

Sahni's work on living plants will be reviewed separately by Dr. P. Maheshwari. But certain palaeobotanical aspects of his early studies cannot be altogether passed over here. One of the questions dealt with in the theoretical part of his publication on Acmopyle (1920a) was concerned with a palaeobotanical matter: the relation of the Cordaitales to the pteridosperms and the conifers. Sahni did not at that time definitely reject the prevailing idea that the Cordaitales were derived from the pteridosperm stock; but he advanced strong arguments against this view and his criticism was later shown to be justified by Florin's comprehensive studies. Sahni's views on various questions relating to the conifers, too, were more in accord with our present knowledge of the oldest fossil conifers than were those of most contemporary authors. In discussing the important problem of the position of the seed in the gymnosperms, he introduced a conception of great general interest from a rialaeobotanical point of view.  On the basis of one single but important morphological feature he suggested a division of the gymnosperms into two groups: “Phyllosperms", with leaf-borne seeds, and “Stachyosperms" in which the seed is seated directly on a normal or modified axis. This distinction - accepted in a morphological sense rather than for practical use in taxonomic classification -is reflected in the views of later workers in phyletic morphology (e.g. Zimmermann, Florin). It has even been extended to apply to the position of all sporangia in vascular plants (" Phyllospory" and “Stachyospory" of H. J. Lam).