The principle objects of investigation were the 19-year-old European and Lubarski larch grafts in orchards and their 2-, 3- and 4-year-old offsprings through free pollination. Visible, actual (0,03% CO2) and potential (0,1% CO2) intensity of photosynthesis; dark- and photo-respiration of adult needles were determined with the help of "Infralit-3". Sugar-content as well as catalytic and peroxidase activity of the needles were also determined. The amount of either-soluble elements in the needles was 4-6%, of starch 6- 9% and ribonucleic acids 28-33 mg %. Both the visible and potential photosynthesis and intensity of photorespiration were in correlation with the biometric parameters of the grafts. Similar correlations were found in their offsprings. Disperion analysis demonstrated the existence of the relation between photosynthesis activity of the needles and the annual increment of the offsprings: in case of 3-year-old European larch plantings the extent of influence was (Formel), whereas in case of 4-year-old Lubarski plantings, it was (Formel). In conclusion, it may be presumed that the ratio of actual photosynthesis to the sum of photo- and dark-respiration might be taken as the basis for evaluation of plus-trees.
