EFFECTS OF ACIDITY ON IN-VITRO GERMINATION AND TUBE GROWTH OF POLLEN FROM DECLINING FAGUS-SYLVATICA

1. Pollen from beech trees (Fagus sylvatica) belonging to different da mage classes was put to germinate in substrates of varying degrees of acidity, 2. As the damage classes increased in severity, the viability and germination of pollen grains was significantly decreased, whereas the length of the pollen tube did not appear to be influenced by the damage class. 3. Cultures in increasingly acid media showed a progress ive inhibition both of germination and of tube growth. 4. No significa nt interaction between damage class and pH was detected for pollen ger mination, while the average growth of pollen tubes from more severely damaged trees appeared to be less inhibited by acidity than material d erived from less damaged trees. 5. In summary, even in the most severe ly affected trees, as long as the culture medium pH did not fall below 4.2, some pollen grains were still able to germinate and to produce t ubes long enough to guarantee fertilization.