The Materials and Methods of Palaeobotany

THE MATERIALS AND METHODS OF PALAEOBOTANY WILLIAM CULP DARRAH 122 Lincoln Hoad, Medford, Massachusetts INTRODUCTION impossible, even ridiculous, duplication of names, creation of artificial form genera, and NDER the guidance of the late establishment of purely arbitrary systems of Prof. Birbal Sahni, the plant-bearing nomenclature. U rocks of India were subjected to Consider but one example of this tendency, scrutiny by every technique known to the Palaeozoic spores and pollens, more precisely palaeobotanist. The most unpromising and called palynology. In utter disregard of controversial sediments were investigated parent sporangia, taxonomic group or bio with complete freedom from prejudice logical origin, the multitudinous forms are (SAHNI, 1941, 1946, 1948; SITHOLEY, 1946). binomially identified, classified, and inter In memory of our lamented colleague, I have preted. Gradually we are erecting a colossus chosen as the subject of this contribution, of meaningless terms which will haunt our The Materiats and Methods of Pataeobotany. synonymies for years to come. The prag New techniques - and improvements of old matic or empirical temporary advantage of techniques - have not only wrought a a workable system for coal correlation and revolution in the interpretation of fossil similar purposes is of little long-range im plants but also have provided methods for portance. Existing techniques are sufficient investigating sediments hitherto considered ly refined and perfected to determine within unwor.thy of attention. the space of a few years the biological Some years ago while turning the pages of identities of hundreds, perhaps a thousand, a venerable tome History of Egyptian Mum Palaeozoic spores and pollens. mies by Dr. Thomas Pettigrew (1833), I The changing views of petrifaction merely stumbled upon a discovery made more than reflect a growing realization of the rela a century before, that bituminization may, tive indestructibility of organic materials under certain circumstances, preserve animal ( DARRAH, 1941 ). The ex cathedra pronounce tissues indefinitely. The similarity between ment "too delicate for preservation" has embalming with bitumens to coalification or passed unchallenged for a century. No bituminization of plant tissue,; convinced me greater obstacle has impeded exploration of that a vast opportunity to investigate fossil new techniques, new approaches to old plants with greater accuracy than heretofore problems, and pioneering in new problems. merely awaits the improvement of known Dr. Pettigrew in 1833 was examining the techniques or the invention of new ones. heart of an Egyptian mummy estimated to During the past thirty years palaeobotany be 3000 years old. He had removed the has tended to fragment into several special bi tuminous embalming preservatives by isms, each with its own methodology and maceration of the heart in " spirits". 'vVithin tradition. Although this is the inevitable a few days the softened tissues began to result of activity and progress, in such decompose and in a week putrefied. The fragmentation there is a loss of coherence. chemical composition of the macerated heart Taxonomic systems become inordinately arti was such that normal putrefaction occurred ficial, terminologies grow complex and the promptly. On several occasions I have philosophy of the science becomes confused. observed thriving colonies of yeasts and Palaeobotany, however narrowly or inclu molds growing on macerated residues of sively we may wish to define it, is the study bituminous coals but in these cases the of fossil plants. This is the only common polysaccharides and "humic" materials of denominator in our chosen field of research. the coals had been fundamentally altered by Yet we have contributed to the separation of prolonged chemical processing. the specialisms by disregarding the nature In order to repeat Pettigrew's observation of fossils. A proper correlation between I sought the co-operation of Dr. Ernest form and structure would minimize the Hootan and Dr. Donald Scott of the Peabody 1+6 THE PALAEOBOTANIST Museum of Harvard University. These Briefly then by 1850, the occurrence of the plant gentlemen provided me with tissues of a embedded plant bodies was not only recog original st female Egyptian mummy and dry mummy niz~d, but also fairly generally understood. denied, w~ Arizona Indian, the former being of the 21st It was known also that resistant cutinized long-stand Dynasty ca. 1000 B.C. and the latter ca. parts could be recovered from lignitic and tion by l\> A.D. 1000. Portions of the pterygoid muscle bituminous coals. masses of from the oral cavity of the Egyptian mummy Solms-Laubach (1891, pp. 2-13) distin by demine were macerated by three methods: mineral guished two types of mineral petrifaction, the Indeed, acids and alcohol, benzene and petroleum first in which there is no organic residue ( i.e. deminerali ether. Well-preserved tissues were recovered all apparent structure is pseudomorphic), silicified " by all methods. On the other hand, no and the second, embedded fossils. This excellent recognizable tissues were recovered from the distinction, which today is recognized as an obvious t dry mummy, which incidentally was not over-simplification, epitomized the results of replacemel impregnated with bituminous substances but Goeppert's extensive investigations. wood was rather was completely desiccated. All these chemical methods involve the Goeppert The preserving qualities of bituminization dissolution of inorganic materials and the form of sil are well known. Forinstance, Bn~gger in pre degradation of organic residues. The degree determine! paring wooden objects found in the Oseberg of chemical alteration resulting from such recognizab Ship used the following technique: wood treatment has long been in dispute and, of Rhynie steamed and soaked with creosote followed by except for certain simple and obvious reac and from a bath in linseed oil in which carbolineum tions, no conclusive evidence has ever been calcareous (an anthracene oil) is dispersed. Soft woods presented. Laboratory experiments on the In this were hardened with alum. This procedure degradation of cellulose and lignin offer little certain cht simulates a common type of fossilization. direct evidence on this question because they yielded all These examples draw attention to the fact do not duplicate natural conditions in which early Pala' that normally destructible tissues have been the organic materials are already degraded. considered preserved by artifactual bituminization and Direct observations on the individual consti Macerat that tissues can be deliberately preserved by tuents of naturally occurring sediments are employed bituminization. extremely meagre. many year For many years the thin ground section to macera MACERATION TECHNIQUES has been respected as the ideal preparation and nitric because, by its very nature, it portrays the sium chlol More than a century ago Goeppert success true condition of the fossil structure. Any vealed the fully removed the petrifying substance of technique which taJ!lpers with the matrix or rials such, silicified and calcified specimens recovering modifies the plant, no matter how little, is and relati" in these experimen ts organic residues of the viewed with suspicion. There is, to be sure, The proce~ original plant bodies. In several cases he a measure of truth in this assumption. has prove( observed the cellulose reaction with sulphuric Certain thin sections, as of the Rhynie chert, The apr acid. Goeppert (1864) performed many the Black Hills cycadeoids and the Permian que to" c( macerating experiments and derived from ferns of Chemnitz, exhibit magnificent pre refinemenl these investigations a better understanding servation. Fungal sporangia, mycelia, sto attempts of the nature of fossils than any other palaeo mata, rhizoids and even cell contents may impressior botanist of the 19th century. As with most be recognized. Yet a silica pe trifaction is COdol1othec prophets, his opinions were generally un oftimes disappointing. Many woods from methods h appreciated. the Triassic of Arizona and the Cretaceous of a large per Other maceration techniques were develop Wyoming preserve nothing of interest, indi which rea ed by several investigators of whom Schultz cating scarcely any features except gross tested for and GUmbel deserve special men tion. form, growth rings, and scattered cell masses. of the bas Schultz in 1855 devised the mixture ·of Such petrifactions are little more than of only a mineral acids (which still bears his name) pseudomorphs. importanc for macerating low rank coals. Subsequent By 1880, despite the work of Goeppert, it on the cal: alkalination was accomplished with sodium was generally assumed that the silicified ( or bryophyte hydroxide. Caustic soda tended to cause calcified) petrifaction was in reality molecular and corda separation of cell masses and, if concentrated, mineral replacement and the structure purely and Arnol dissolved certain constituents. GUmbel mini pseudomorphic. Chemical analyses disclosed oPteris. ' mized this disintegration by gentle alkalina insignificant carbon content, a fact which was b'e recove tion with ethyl alcohol. in terpreted as proof of the disappearance of shown in: DARRAH - THE MATERIALS AND METHODS OF PALAEOBOTANY 147 :urrence of the plant body. The possibility that the TRANSFER TECHNIQUES only recog original structure could be present while not It has been assumed generally that such mderstood.

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