The Feulgen reaction and the staining of preparations with two DNA-specific fluorochromes, Hoechst 33258 and 4 ′ ,6-diamidino-2-fenilindol (DAPI), were used to study the preservation of DNA in the fossilized leaf and fruit tissues of the Lower Eocene Myrtaceae, Paramyrtacicarpus plurilocularis and Paramyrtaciphyllum agapovii collected in Yakutia (Siberia, Russia). It was shown that chromatin structures of the fossilized plants form stable red-purple complexes with the Schiff's fuchsin sulphuric acid reagent in situ . This coloration is specific for DNA, in particular, for the deoxyribose residues. It means that the cell nuclei of these 53-55 Myr old plants preserve a part of the deoxyribose backbone of DNA molecules. On the other hand, there was no, or only a very weak, staining of the cell nucleus with fluorochromes DAPI or Hoechst 33258, which specifically bind to the double-stranded DNA and do not bind to either the single-stranded DNA or RNA molecules. The stainability of fossil plant cell preparations with alcian blue shows that there are also polysaccharides containing carboxyl groups in the cell walls of fossilized leaf and fruit tissues of the Lower Eocene Myrtaceae.

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Structure of the multiple archesporium in an ovule, time and place of archesporial cell differentiation and their developmental potential have not been studied in detail. In Paeonia species supernumerary archesporial cells are formed and differentiate as multiple megasporocytes, but only one embryo sac usually develops into an ovule. The reasons leading to development of one gametophyte and the death of most megasporocytes are unknown. The morphological structure of the multiple archesporium in Paeonia veitchii and P. caucasica was studied using cytoembryological methods. We used staining with aniline blue and fluorescence microscopy for visualization of callose on the megasporocyte walls. All cells of the ovule in investigated Paeonia species are uniform and meristematic at the earliest development stage. The onset of archesporium differentiation correlates with inner integument initiation. The sporogenous complex includes ten to 25 cells which develop asynchronously. The cell located in the central part of the sporogenous complex is differentiated into a megasporocyte earlier than in neighbouring cells. Only this megasporocyte is enveloped in callose; it develops further through to meiosis and forms a female gametophyte. The other megasporocytes degenerate during ovule development. We consider that callose participates in the mechanism of ‘lateral inhibition’ during megasporocyte maturation. The cell located in the central part of the Paeonia ovule is the first to receive signals that stimulate the onset of megasporogenesis and formation of the callose wall. It is possible that callose participates in blocking of development signals to neighbouring megasporocytes, leading to the arrest of their development.

Fruit morphology and the anatomical structure of the pericarp, fruiting perianth, and seed coat were studied in 15 species of Poikilospermum, a genus whose position within the Urticaceae has long been controversial. Possible evolutionary trends of their transformation are suggested for both subgenera; plesiomorphies were found in P. oblongifolium and P. scabrinervium. Structural peculiarities of the fruit connected with its ejection out of the tubular perianth are discussed. The archaism of the fruit in Poikilospermum is revealed, indicated, as in Boehmeria, by the presence of the rudiment of an aborted carpel in the form of a large two-lobed rib. Using carpological anatomical characters, the species studied are classified into informal groups, such characters being able to pull the species within the subgenera into rough groupings where gross morphology has been unable to do so. It is shown that heterobathmy may be strongly associated with the genus Poikilospermum. Each subgenus has its own set of primitive carpological characters: in subgenus Poikilospermum the absence of a fruiting perianth which encases the fruit, and also of capitate inflorescences with swollen receptacles; in subgenus Ligulistigma remnant rudiment of the second carpel and ovary loculus, as well as a primitive, less simplified seed coat. Though the position of Poikilospermum as indicated by molecular data is within Urera, our results suggest that Dendrocnide (the only genus of the Urticeae that has a pyrenarium fruit type) may be closest to Poikilospermum, although the pericarp structure and dissemination behaviour in Poikilospermum are more specialised than those exhibited by Dendrocnide. Seed coat structure is also shown to exhibit traits seen in Moraceae.

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