Some characters of the pollen of spring and summer flowering common oak (Quercus robur L.)

Summer flowering of the common oak is a natural rarity, considering the large area of the species natural distribution. This phenomenon can be classified as an ancestral (atavistic) property. Pollen morphological and physiological characters from spring flowering male inflorescences collected over the period 2004 - 2007 and summer flowering male inflorescences collected in 1999 were compared. The analysis included the pollen of a tree with frequent summer flowering and a control tree with spring flowering only. The size and form of summer pollen differed from the spring flowering pollen. The germination percentage and germination energy depended on the pollen growing medium (0, 5, 10, 15, 20, 25% sucrose solution), year of collection (2004 - 2007), temperature (+5°C and -20°C) and storage period (1 to 24 months). The study results are significant for the explanation of common oak phylogenetic development, and they contribute to the knowledge of pollen characters under the effects of different factors.