Normally only one tube develops from a pollen grain. In polysiphonous grains however more than one tube may emerge from a grain up to 10 pollen tubes have been observed in Althaea rosea and 14 in Malva neglects. As a rule only one of them makes further growth in lants where pollen grains are united into tetrads or pollinia several pollen tubes are produced at the same time and all of them may grow. Branching of pollen tubes is quite common in the members of some Amentiferae.

The first requirement of pollen germination is their hydration which takes from a few seconds to a few minutes. This induces the activation of the inactive cytoplasm of the pollen grains. Many cellular organelles undergo considerable changes in comparison to what has been observed in inactive ripe pollen.

Activation of pollen grain does not induce any change in mitochondria, lipid bodies, generative cell and vegetative nucleus.

Factors involved- carbohydrate, Boron, Ca, enzymes, Hormones and physical factors.

Pollen tube germination time- 30-40 minutes-Lilium due to large amont of sucrose.