The research involved the examination of inter- and intra-population variation of stomatal traits: stomatal density, stomatal length and width, stomatal pore surface, potential conductance index and stomatal shape coefficient, in Quercus robur L. leaves. The research was conducted in northern Serbia and included five populations (?Ada Ciganlija?, ?Bojcinska suma?, ?Subotica?, ?Sombor? and ?Vrsac?). The stomatal characteristics were examined in fully expanded leaves, from two leaf positions - the sun-exposed and shaded side of the tree. The leaf position in the tree crown, forming a part of the phenotypic variance, was relevant for the stomatal dimension traits. Within populations, the differences between the genotypes (i.e. trees), were relevant for all analyzed traits. On the basis of the analysis of the inter-populational differences, the ?Bojcinska suma? population had a statistically significantly lower stomatal density in comparison to the other populations.

The chemical composition of the essential oil of the needles and twigs of dwarf pine (Pinus mugo Turra) growing wild in Serbia was investigated. The oil was analysed by GC/MS and the major constituents found were δ δ δ δ δ-3-carene (23.9%), α α α α α-pinene (17.9%), β β β β β-pinene (7.8%) and β β β β β-phellandrene (7.2%).

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Most commonly used morphological attributes were correlated with nutrient concentration in order to standardize quality assessment of two-year-old hop hornbeam (Ostrya carpinifolia Scop.) seedlings. Diameter has proven to be the best single morphological indicator of seedling quality given its strong positive correlation with all other observed morphological attributes. Seedling dry mass (shoot and root dry mass) and Dickson Quality Index can be considered the most comprehensive indicators of hop hornbeam seedling quality. However, the measuring of mass is destructive and requires a certain amount of time. The absence of strong correlations between physiological and morphological attributes of two-year old seedlings of hop hornbeam suggests the need for further research. The only significant correlation between physiological and morphological attributes (weak and positive) was recorded between the potassium concentration in root and root collar diameter after the second growing season. [Projekat Ministarstva nauke Republike Srbije, br. 43007: Studying climate change and its influence on the environment: impacts, adaptation and mitigation

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