bild

Pollen production. Cloud of pollen (white) from a male flower (catkin, upper left) settling on a female flower (red stigma, lower centre) on a hazel plant (Corylus avellana). Wind pollination is known as amenophily. To be successful, it requires vast quantities of pollen grains to be produced. A single hazel catkin is estimated to produce up to four million grains of pollen. Successful pollination leads to the formation of a seed (here a hazelnut) that may form a new plant. Wind-borne pollen is the principal cause of hay fever in humans. (KEYSTONE/SCIENCE PHOTO LIBRARY/DR JEREMY BURGESS/SCIENCE PHOTO LIBRARY)