Microsporogenesis and microgametogenesis of Rhododendron ledebourii (semi-deciduous), Rhododendron luteum (deciduous), and Rhododendron catawbiense (evergreen) were studied by light and electron microscopies in order to determine the stages of pollen development in relation to period of winter dormancy and bloom time throughout an annual growth cycle. Development of generative organs starts in June in R. ledebourii and in July in R. luteum and R. catawbiense and reaches completion about 11 months later. R. luteum and R. catawbiense microspores undergo meiosis at the end of the August and spend winter at the vacuolization stage. Mitosis with the formation of bicellular pollen grain occurs shortly before flowering at the beginning of June. R. ledebourii develops two types of flowers which differ in the timing of microgametogenesis. The first type is characterized by early microspore meiosis and mitosis leading to development of bicellular pollen grains by the end of August, and is prone to fall blooming during warm autumn temperatures. Microspores of the second flower type have a more prolonged vacuolization stage with mitosis and subsequent bicellular pollen grains occurring in November. By winter, flower buds in R. ledebourii are more advanced developmentally than in R. catawbiense and R. luteum, and bloom about 1 month earlier. The different strategies of pollen development identified both within and between these three Rhododendron species were recognized which are not associated with leaf drop during winter but appear to be related to the time of spring flowering and the frequency of autumn flowering.

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Botanic gardens with their rich collections and scientific resources have a unique potential that attracts the attention of the society to the problems of preserving biodiversity, ensuring environmental education, conserving nature, providing leisure, serving the place for relaxation and entertainment. One of the oldest Botanic gardens of Russia is the Saint Petersburg Botanic Garden of the Komarov Botanic Institute of the Russian Academy of Sciences demonstrates the experience of utilizing the open ground collections for Botanic and environmental education. The experts share various aspects of interaction between a Botanic garden and its visitors. The paper provides examples of excursions and other forms of work on the open ground. The paper analyzes the experience of foreign colleagues related to the motivation for visiting Botanic gardens by different age and social groups. The authors provide data of sociological surveys of visitors and the analysis of their motives to visit the Saint Petersburg Botanic Garden in particular. It also shows the growth of interest in the open ground collections.

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