The ESEM investigations revealed the morphogenesis of peltate glandular trichomes, which was divided into five phases. In phase one, new peltate glandular trichomes were initiated; in phase two, they were differentiated; in phase three trichomes grew vigorously; in phase four they were determined; in the fifth and final phase they came to maturity. Volume of glandular trichome during the different phases of morphogenesis varied from 0.25´10 -2 mm 3 in phase 1, to 1.95´10 -2 mm 3 in phase 5. More glandular trichomes are placed on the base of the adaxial side of bracts (average 7 mm -2 ) than on the base of abaxial side (average 5.8 mm -2 ). In this research, positive Spearman's rank order correlations were found between the average number of glandular trichomes and content of a-acids as well as between the average volume of glandular trichomes and content of a-acids.

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An ecogeographical survey of wild hop populations was conducted in the northwest of Croatia in two consecutive years. A total of 121 plants was documented on eight locations. Along with the passport data, the data on three phenotypic traits (no. of leaflets, cone shape, aroma) were gathered during collection, while the content of α-acids in hop cones was determined by lead conductance. Shannon's information index was calculated for each phenotypic trait and was used as a measure of intra-and inter-population diversity. For all analyzed traits, most of the total phenotypic diversity was attributable to differences among plants within populations. The differences in proportions of individuals having a particular trait state between all pairs of populations in the case of leaflet number and cone shapes were non-significant. Four out of 28 pairwise comparisons for aroma were proven significant, indicating the existence of differences in proportions of individuals across populations recorded to have 'typical hoppy' , 'fine hop' or 'rough' aroma. No significant differences were observed for α-acids content among populations. Plants exhibiting elongated cone shape had significantly higher α-acids content than those having oval or round cone shapes. Similarly, plants categorized as 'rough' aroma hop cones had the highest content of α-acids compared with those categorized as 'typical hoppy' or 'fine hop aroma' hop cones.

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The results of this study show that the most usual damages of hop glandular trichomes are obtained on tunica of peltate glandular trichomes as well as cracking of bulbous glandular trichomes. In fresh hop cones any sorts of damage of glandular trichomes are obtained, on the other hand frequency of damaged hop glandular trichomes increase after drying (f i =0.08) and after pelletization of hop cones the structure of glandular trichomes is completely destroyed. Volume of hop glandular trichomes of dried hop cones is significantly smaller in the comparison with volume of glandular trichomes of fresh hop cones (D=0.544×10-2 mm 3 ; P<0.01) and a phenomenon of shrinkage on tunica surface of peltate glandular trichomes of dried hop cones is also visible in comparison with the fresh one. The decrease in volume of hop glandular trichomes in dried hop cones is the result of dehydration of hop cones and consequently hops glandular trichomes during the drying process which cause shrinkage of peltate glandular trichomes. However, after pelletization the structure of hop glandular trichomes is completely destroyed.