IN THE autumn of 1819, a London doctor called John Bostock published an account of "an unusual train of symptoms" from which he suffered periodically - itchy and watery eyes, a runny nose and persistent bouts of sneezing Once identified, the ailment was observed to be a prevalent one, and for many years afterwards was known to the medical fraternity as "Bostock's Catarrh". Then it was discovered that the condition was an allergic reaction to pollen in the atmosphere and that pollen from the various grasses was the worst offender - and so it became "hay fever".
Because plants are rooted in the soil, they have had to develop a rather different means of procreation than that employed by human beings 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 be carried for hundreds of miles the grains themselves are small, smooth and streamlined to maximise their gliding ability, and some varieties even have little air bags to help them stay afloat.
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 in June and early July - and there the problem lies for those of us who are allergic to the substance.
The whole process 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 detaches the pollen from the pollen sacs. 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: a shower of rain when the pollen count is high "washes out" the atmosphere, and reduces concentrations quite dramatically.
As it happens, the average amount of pollen in the summer air has fallen in recent decades. Farmers have switched from hay to silage as a feed for cattle and silage making requires that the grass be harvested before it flowers. And yet the incidence of hay fever appears to be increasing for reasons of which no one is entirely sure.