On two-year-old seedling plants of genus Betula it is shown, that a silver birch and a downy birch already at early stages ontogeny, differ among themselves on strategy of distribution metabolite. At silver birches of both forms the bulk of assimilates are directed toward trunk tissues to satisfy cambial growth demands. Formation of conducting system goes on a background of the high metabolic status. At a usual silver birch accumulation of carbohydrates results in formation of thick-walled vessels of xylem with strong lignified cellular walls. At the Karelian birch intensive accumulation of saccharose in phloem can break cambial activity, resulting in the future to formation of structural anomalies of wood. At a downy birch the attracting cent of photoassirmlate the crone is fluffy. Accumulation of carbohydrates in leaves can lead to decrease in intensity of photosynthesis and as consequence to reduction of intensity of transpiration and water-conductivity of xylem. In result, in a trunk are formed less lignified cells of xylem, in comparison with a silver birch.