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Pyritized twigs and roots from the Eocene London Clay of SE England were studied to gain a better understanding of the process of pyritization by investigating pyrite textures in relation to cell type and quality of preservation. Highly polished sections and fractured surfaces taken from 124 specimens were examined using optical microscope and SEM, the latter equipped to map pyrite and carbon. Pyrite textures include microcrystalline, framboidal, massive polycrystalline, and subhedral or euhedral forms. The highest fidelity of preservation is always associated with microcrystalline pyrite precipitation on wall surfaces with subsequent infilling of cells with framboids or polyhedra preventing compression during burial but contributing nothing to actual ultrastructural preservation. Ultrastructurally, parenchymatous cell walls are coalified, whereas microcrystalline pyrite plus coalified material were observed within lignified cell walls, in all, four stages of pyritization are documented. Observations are interpreted in the light of recent experiments on pyritization of living material and the chemistry of pyrite formation in anoxic environments involving an aqueous, and hence mobile, les cluster complex as a precursor. The complexity of the fossilization process is reflected in the presence of different textures in adjacent cells of the same tissue. This demonstrates the development of isolated chemical microenvironments as pH and Eh vary in response to decay, and mineralization and pyrite overgrowths within a cell indicate local microenvironmental changes through time. Keywords: London Clay, pyrite, plants, preservation.

The process of fossilization is poorly understood. However, it is central to our understanding of the evolution of life. It is unclear how plant tissues become fossilized, whether fossilization is selective to specific biopolymers, or whether original organic constituents survive. We have replicated the fossilization process in the laboratory by using both microbial and chemical approaches to pyritize plant debris. These results demonstrate that initial pyritization can be an extremely rapid process (within 80 days) and is driven by anaerobic bacterial-mediated decay. Initially, pyrite precipitates on and within plant cell walls and in the spaces between them. Further decay and infilling at all scales preserves broad cellular anatomy. The results have implications for fossilization in general and the fidelity of the taxonomic and biomolecular information preserved in fossils. Keywords: pyrite, plant, fossil, synthesis.

Epidendrum, the largest genus of Neotropical orchids, contains both nectar-secreting and nectarless species. Here, we compare the fine structure of the inner floral spur, termed the cuniculus, in nectariferous (E. difforme, E. nocturnum,E. porpax, E. rigidum, E. vesicatum) and seemingly nectarless (E. capricornu, E. ciliare, E. criniferum, E. pseudepidendrum, E. radicans, E. xanthoianthinum) species. This is the first time for such a detailed investigation of cuniculus structure to be undertaken for Epidendrum. Our aim was to characterize features indicative of secretory activity and to ascertain whether flowers presumed to be nectarless produce alternative pollinator food-rewards. The cuniculus is formed by fusion of the basal part of the labellum and column and extends alongside the ovary and transmitting tract. Our study indicates that all investigated species produce nectar or nectar-like secretion to varying degrees, and no alternative pollinator food-rewards were observed. Even though macroscopic investigation of presumed rewardless species failed to reveal the presence of secretion within the cuniculus, close observations of the cells lining the cuniculus by LM, SEM, and TEM revealed the presence of cuticular blisters and surface material. Moreover, the similarity of both the thick tangential cell walls (with the exception of E. vesicatum) and organelle complement of cuniculus epidermal cells in both copiously nectariferous species and those producing only small quantities of surface secretion confirmed the presence of secretory activity in species generally regarded to be rewardless. The secretory character was particularly obvious in the cells of the cuniculus of E. nocturnum, but also in E. ciliare, E. radicans and E. xanthoianthinum, since electron-dense cytoplasm and mitochondria, ER and secretory vesicles were abundant. Furthermore, cell wall protuberances occurred in E. nocturnum, which was indicative of intense transmembrane transport. This investigation highlights the need to examine more closely whether Epidendrum spp. considered to lack food-rewards based solely on macroscopic examination really are rewardless and deceptive. [ABSTRACT FROM AUTHOR]

Although many Orchidaceae have deceit flowers that produce no reward, the most common reward, when present, is nectar. Bulbophyllum, however, is unusual in that the labellar secretions of most species investigated to date lack sugars, and, therefore, cannot be considered true nectar. The African species Bulbophyllum saltatorium is an exception in that it produces not only nectar but also possesses specialized, capitate oleiferous trichomes. The nectary of B. saltatorium is borne on the labellum and is represented by a deep, narrow, median longitudinal groove, having a small aperture, and flanked by trichomes. Isodiametric epidermal cells lining this groove secrete nectar which collects both in the groove and on the surface of the labellum. As well as a nectary, the labellum of B. saltatorium also bears three types of unicellular trichomes: the longest trichomes are borne distally and abaxially; the marginal ones form a rim around the entire labellum, and finally, massive, capitate trichomes occur proximally and adaxially. These are oleiferous, containing large quantities of oil which might function as precursors of volatile components of fragrance or provide a food-reward. To the best of our knowledge, this is the first time for such oleiferous trichomes to be described for Bulbophyllum. Therefore, apart from their color and markings, flowers of this species are able to attract pollinators in at least two, possibly three ways: food-reward in the form of nectar; fragrance; and possibly food-rewards in the form of food-hairs. [ABSTRACT FROM AUTHOR]