In the reported studies, an attempt has been made to determine the proportions and causes of empty seed production in European larch. All experiment were carried out on 25 clones growing in the Kornik seed orchard. Observations on pollination, megasporogenesis, fertilization and embryo development have shown the amount of seed degeneration at different stages of development. The aim of the controlled pollination experiments has been to discover the genetic reasons of empty seed production. Investigations of the enzymatic systems were an attempt to explain the genetic load in relation to genetic polymorphism. It was established that 1. Synchronization of pollen dispersal and female flowers receptivity was sufficient for adequate pollinatin of female strobili on the observed clones. 2. The longer was the period of female flowers pollination, the greater was the full seed production. 3. Efficiency of open pollination varied from 60% to 99%. Lack of pollination reduced the potential number of filled seeds on average by 17%. 4. An increase in the number of pollen grains per ovule favourable full seed production by reducing the negative effect of genetic load. However there was no significant correlation between the amount of polyembryony and the proportion of filled seed. 5. Physiological disturbances in female gametophyte development increased empty production by about 9%. 6. Pollen remaining in the micropylar canal and lack of pollen germination on the nucellus, due mainly to inviability of pollen, increased the proportion of unsound seed on average by 17%. 7. After open pollination, embryos degenerated in 47-75% of fertilized ovules, which increased the amount of empty seed on average by 30%. Embryo degeneration has mainly genetic reasons. 8. In general, the average yield of full seed after open pollination becomes about 27%. 9. The negative effect of self-pollination on filled seed yield have been found to operate after fertilization, during the early stages of embryo development. After controlled self-pollination embryo degeneration took place in 85-100% of the pollinated ovules. 10. Out of 29 observed clones, on 2 only the pollen dispersal has been finished before the onset of female strobili receptivity, thus limiting the possibility of self- pollination to a minimum. 11. In spite of the great amount of embryo degeneration, the estimated relative self-fertility indicates, that in relation to other conifer species larch has a proportionaly high possibility of full seed production after self-pollination. 12. Negative genetic load estimation as the number of embryonic lethals is rather low. 13. The great number of unsound seed coupled with the low number of embryonic lethals may be caused by the negative genetic load, only if one assumes that the few embronic lethals exist throughout the population with a high frequency.
