Plants, because they are rooted in the soil, have had to develop a rather different means of procreation than that employed by you and me and other animals: they have to use a go-between.
Some make use of unwitting insects for this purpose, but others scatter their pollen to the wind, and hope that it will be carried to a destination that ensures fertility. Once aloft, pollen can travel large distances, since the grains are small, smooth and streamlined to maximise their gliding capability.
Obviously the chances of a single pollen grain hitting a recipient flower of the right species are extremely small, so plants enhance their chances of success by exuding many millions of such grains in favourable conditions. Their activity reaches a maximum with the approach of summer, and there the problem lies for those who are allergic to the pollen spores from various grasses, those who suffer from hay fever.
The incidence of hay fever is very dependent on the weather. Firstly, the rate of extrusion of pollen by plants is related to the temperature, increasing as the air gets warmer. Wind strength is important, too, because the moving air carries the pollen from its place of origin.
The "stability" of the atmosphere plays a part, because in showery conditions, with vertical currents in the atmosphere, the available pollen is dispersed through a deep layer of air, reducing the count near ground level.
And perhaps the greatest influence is rain, since a shower of rain when the pollen count is high "washes out" the atmosphere, and reduces concentrations quite dramatically.
But regardless of the ambient pollen count, hay fever is strangely selective in its victims. Most likely to be affected are children between five and 15 years old; after 30, most sufferers find themselves less troubled by it.
It affects more boys than girls in the younger age groups, but in mature people more women than men have problems with the ailment. Moreover, the oldest child in a family is four times more likely to suffer from hay fever than the youngest, and children born in the spring are more susceptible than autumn babies, - which suggests that exposure to pollen in the first few months of life may be a disadvantage.
It is also true, it seems, that hay fever has become more common in recent decades. Part of the increase in reported cases can be attributed to greater public awareness of its existence and to a growing tendency to consult a doctor for minor ailments.
But it is also believed that higher levels of pollution in the atmosphere may have some bearing on the matter.