The hierarchical structure of the thallus of the brown alga Cystoseira barbata from the Black Sea and the relationship between the structure and apparent photosynthesis were studied. The thalli were selected for measurements in different months of the year from three regions of the Crimean shore. The morphological analysis was successively carried out at several levels of the thallus's structure: at the level of axes of different orders, at the level of separate branches, morphological divisions (sum of the main branches, sum of the adventitious branches, the stem) and the whole thallus. The following parameters were measured and calculated for all levels: weight, water content, ash, organic carbon and chlorophylls and c in biomass, surface area, relative surface area, relative (specific) and total photosynthesis (evaluated by the radioactive carbon method). Proceeding from the axial analysis, the authors suggest an example of the determination of morphological and physiological parameters of the whole thallus at the age of 2.5 years.Results of the measurements and calculations revealed that properties of the axes of different orders are essentially different. Properties of the axes of different orders, their number and proportion are in their turn responsible for the properties of the higher levels of the organization of the thallus (branches, divisions, whole thalli). Besides, the axial analysis provides knowledge on the morphophysiological condition of the plant and allows to calculate the carbon flow through the thallus and the population. The axial analysis enables to evaluate the effect of contamination on a certain species and its population. Methodological aspects of the axial analysis are also discussed.In the previous work (Khailov 1979) the structure of the Cystoseira thallus and its transformation in ontogenesis were described in terms of the main and the adventitious branches. However, branches are complex and variable per se. It was formerly shown that their carbon exchange with the environment is determined by the ratio of more elementary structures of different age . The axes of different orders are elementary structures which cannot be subdivided any further. So in the present work we have carried out the axial analysis of the main and the adventitious branches.
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