DEVELOPMENTAL RHYTHMS AND STRUCTURAL AND FUNCTIONAL SPECIFICITY OF <i>DRYAS OCTOPETALA (ROSACEAE)</i> LEAVES
A comparative research of developmental rhythms and structural and functional specificity of <i>Dryas octopetala</i> leaves has been done. The leaves of spring generation are kept the functional activity during one season, their lifetime lasting 1.5-2 months. The leaves of autumn generation begin their development in August, survive winter under snow cover and continue working throughout next vegetation season. Their total lifetime is 11-12 months. Different organization of mesophyll and terminal phloem was found in leaves with different development rhythms. Higher rate of spring leaves development is associated with formation of the apoplastic labyrinths of their cell wall in the zone of phloem loading. The structures are related with intensification of formation and functioning of apoplastic channel of photosynthate export. These structures are missing in the leaves of autumn generation vegetating for two seasons. In winter time, the plastid agglutination in their mesophyll, and obliteration of sieve tubes in their phloem are usual. Both are signs of photosynthetic pause in winter time. By the sum of the studied signs, the leaves of spring generation are similar to seasonal leaves of herbs, and the leaves of autumn generation to perennial leaves of evergreen forms. The combination of the two leaf types with different rhythms of development in one plant is an evidence of plant life-form transfer from woody to herbaceous in relation to plant glaciophylia.