SUMMARY -The early phases of basidiospore-derived infection of Me/ampsora pulcherrima (Bub.) Maire on the leaves of Mercurialis annua L. were studied by light microscopy, SEM and TEM. The fine morphology of the basidiospore germling penetration and intraepidermal infection structures is discussed in comparison with that of other rusts recently described. The direct penetration through the epidermal cell wall, characteristic of the rust basidiospore-derived germlings, is confirmed. The absence of an extrahyphal matrix around the intraepidermal vesicle and the presence of a collar around the vesicle neck are pointed out.

Archaeological excavations in Florence (Italy) offered the opportunity of collecting archaeobotanical data along stratigraphic sequences and pits from late Roman to Middle Ages; until now, no archaeobotanical data of this range of time were available for Florence. To achieve a more comprehensive reconstruction of the antique landscape and of the plant uses in the city, the results of plant micro-and macro-remain analyses were compared. During the late Roman Period, mixed oak forests covered the surrounding hills, while only scattered riverine thickets grew in the Arno river plain, which was mostly open. In the city, the increase in richness of cultivated plants, weeds and ruderals follows the advancement of urbanization from the late Roman to the Middle Ages when the abundance of remains of cereals, figs, grapevines and other fruits showed that cultivation and/or food processing were performed close to and even within the town wall. Peaks of heather (Erica spp.) pollen suggested that its flowering branches were introduced in the site and possibly used as building material or for the maintenance of the Arno river bank. Thus, this integrated archaeobotanical approach provided new insights into the environmental and ethnobotanical history of Florence, highlighting the occurrence of horticulture within the city wall.

A cyto-histological study was carried out on Pinus sylvestris seedlings artificially infected with basidiospores of Melampsora pinitorqua and Melampsora laricitremulae, in order to differentiate between the two rust fungi and delineate their taxonomical relationships. The general morphology of the early phases of the majority of infections of Melampsora larici-tremulae on P. sylvestris show similar characteristics to those of M. pinitorqua. Moreover, in M. larici-tremulae / P. sylvestris interactions, the following were the specific characteristics: abnormal germlings and secondary basidiospore production, «cell wall-like appositions» encasing the fungal structures in the host, necrosis of the infection structures, necrosis of the host tissue colonized by mycelium from epidermal to parenchymal cells. Such reaction types reveal the coexistence of pre-and posthaustorial defence mechanisms, typical, respectively, of a nonhost and host resistance. This coexistence which is useful in understanding the evolution of this host-rust interaction, was examined. The described defence mechanisms of P. sylvestris vs. M. larici-tremulae could indicate that the two rust fungi are still closely related entities, however diverging, which evolve from «formae speciales» to «species».

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