#Spore biology free

Two basic forms of spore are recognised based on the original relationship of the spore tetrad when in the sporangium. Spores, in the broadest sense, are produced in the life cycles of so called 'lower plants' or cryptograms, comprising algae, fungi, bacteria and the extensive array of seedless metaphytes. They are particularly valuable in freshwater environments, in evaporitic deposits and situations where marine and freshwater facies interdigitate. While botanical information from them may be limited, fossil spores and pollen have proved exceptionally useful as biostratigraphic indices. The angiosperms produce pollen with the greatest morphological variation, but typicaly with either a tricolpate or monosulcate form.(See Biology below). pollen with one, two or rarely three air sacs attached to a central body (colpus) or monosulcate pollen as in the cycads and ginkgos. Recent gymnosperms may produce very distinctive saccate pollen, i.e. The early gymnosperms produce prepollen, differentiated from true pollen by germination from the proximal rather than the distal side. Because of their relatively simple genetic systems plants may utilise hybridisation and self fertilisation. It should also be remembered that higher plants have charcteristics of reproduction which permit them to utilise modes of evolution unavailable to animals. The trilete and monolete marks imparted on the individual spores are the marks where each of the spore tetrad once abutted each other.Ĭlassification of pollen, like that of spores is based on the morphological trends observed among various groups of fossils which may be primarily but not entirely reflections of evolution within the groups of plants which produced the pollen. The important feature of homospory in terms of the fossil record is the four fold division involved in spore production, this takes the form of either a tetrahedra which gives a trilete spore or a tetragon which gives a monolete spore. mosses and liverworts, and the Pteridophytes which, although not a natural classification, encompassess all the seedless vascular plants, including the palaeontologicaly important ferns and fern allies, are primarily classified using the gross morphology, wall structure and the type of wall sculpture, if present.

#Spore biology free

The free sporing plants including the Bryophyta e.g.

The fact that spores and pollen are normally retrieved from their host sediments as disjunct entities, separate from the original parent plant means that their natural affinities are often obscure. The angiosperms did not appear untill the early Cretaceous and diversified rapidly from the mid Cretaceous. The earliest gymnosperms appear in the very latest Devonian and rapidly become diverse and important during the Carboniferous. Both these forms of plants relied on water (or at least damp conditions) to allow transport of the spermatozoid to the egg. By the end of the Devonian heterospory had appeared, this still involves dispersal by spores only but both microspores (held in a microsporangium) and megaspores (held in a megasorangium) are produced. The earliest terrestrial plants are recorded from the late Silurian, and these were homosporous (all spores produced are of the same kind). Perhaps the greatest contribution made by a single person was that made by another Swede, Gunnar Erdtman, who from the 1950's to the 1970's produced several classic books and papers which remain required reading today. In Britain during the 1930's Raistrick used spores he recovered from coals to recognise different coal seams, but he did not name the spores he found but assigned them an alpha-numeric code.

He studied tree pollen preserved in peat to build a picture of fluctuating climatic conditions during the Quaternary. One of the very earliest practical applications of preserved pollen in the reconstruction of changing environments was by the Swedish palynologist Von Post in 1917. Observations of pollen by Grew and Malpighi are recorded from shortly after the invention of the microscope in the mid 17th Century. Pollen of seed plants, both angioperms and gymnosperms increasingly dominate palynological assemblages of Mesozoic and younger nonmarine deposits. Spores are produced by the so-called 'lower plants' or cryptogams, and within this group the pteridophytic vascular plants and bryophytes (mosses, liverworts and hornworts) are the most commonly studied. The initial meaning has now been expanded to include all acid-resistant organic microfossils. Most fossil spore and pollen grains are studied in a dispersed state and this is the fundamental basis upon which Hyde and Williams (1944) initially proposed the term Palynology. Terrestrial plants produce extremely resistent spores and pollen which are easily transported by wind and water. In general the spores of bacteria, fungi, algae and protists are rarely preserved but those of terrestrial plants are very common fossils.