Examined the influence of increased acidity on pollen germination and growth of pollen tubes of woods. A direct influence is gradually shown only beginning with the values of pH 3.6. Most sensitively reacts the pollen of Abies alba and, thereafter, that of Quercus robur, with a threshold value of pH 3.0. Pollen of Picea abies showed at this value a percentage of germination of 75%, that of Pinus sylvestris 81%. Length of pollen tubes was not significantly influenced. Pollen of Pinus sylvestris showed partial germination even at pH 2.6.