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In the process of plant reproduction, when a pollen grain that transports male gametes lands on the stigma of another flower, it initiates the formation of a pollen tube.

Normally, a pollen grain that sticks to the stigma of a flower during pollination germinates into a long tube that grows straight and unbranched through the ovary to the ovules, where fertilisation takes place.

Through painstaking analysis of each pollen grain under the microscope, they found a record of forest changes spanning 850 years, covering both the onset of the Little Ice Age around 1400 and the arrival of European settlers and subsequent intensive logging practices around 1650.

But authors of this study say measuring allergen levels instead will be more accurate as each pollen grain can release a different amount of allergen each day, and it is the allergens in the air that are primarily responsible for causing hay fever symptoms.

Research is ongoing to see whether regular measurement of allergen levels can become the standard in the UK, and whether there are other environmental factors, such as meteorological factors including temperature, wind, humidity, and air pollutants, that influence how much allergen each pollen grain releases.