OF THE three types of hay fever you are probably least familiar with that which is caused by tree pollens during the spring. This is to be expected because this type is the mildest of the three. Most persons are not even aware of the fact that they are allergic to the tree pollens. But if you have had hay fever for more than four years, the chances are pretty high that you are caused to sneeze and sniffle by one or more kinds of tree pollens. The symptoms rarely last long nor are they generally very severe. Because of the mildness of the symptoms, which consist of a few sneezes, sniffles, and itching eyes and nose, you are likely to mistake them for an oncoming cold. And when the symptoms last for so short a period, you are led to believe that you successfully prevented the occurrence of a full blown cold with its harsh after-effects.
The relatively small number of tree pollen sufferers, and the mildness of the symptoms, is probably due to the fact that the offending trees are not as abundant nor as widely distributed as the grasses and weeds which are responsible for hay fever. The symptoms resulting from tree pollen sensitivity are often associated. with your local environment. For instance during the tree season you may only experience sneezes or sniffles at home, on your way to the train, near your office, or in some other locality where the particular trees responsible for your discomfort are located. Many cases of this type are reported by physicians whose patients live in the suburbs and work in cities.
DURATION OF SPRING SYMPTOMS
The period of duration of spring hay fever symptoms varies in each person with the different kinds of tree pollens to which they are sensitive. And it has been shown that if you are allergic to one member of a species you will be sensitive to other members of that species. For example, if the pollens of the silver maple bother you, it is likely that the pollens of red maple and sugar maple will cause you discomfort. Further, if you are sensitive to more than one kind or genus of tree, your symptoms will be accordingly extended. For instance, if you are affected by the pollens of maple, elm, and oak trees, you will experience symptoms during late March and early April when the maple and elm pollinate. Later, you will again experience symptoms at about the middle of May, when the oak trees pollinate. But if you were allergic to oak only, you would have no symptoms until mid-May.
PERIODS OF TREE POLLINATION
The length of time during which the symptoms last also varies with the time it takes for the particular trees to pollinate. Fortunately for hay fever sufferers most trees seem to hurry through the process of pollination. In some cases they may complete the act of pollination in one day. The stamens and pistils can be seen to wither within twelve hours after the characteristically minute tree flowers have reached full bloom. If you watch the trees in your neighborhood, in some of them you will be able to see the appearance and disappearance of the relatively insignificant flowers over a period of only five to ten days. Soon thereafter you will see the growth of leaves. Most trees pollinate before their leaves come out. Thus, contrary to popular opinion many trees are in bloom while they are bare of leaves. That is, if we continue to use the expression “in bloom” as applying to the time when the flowers are ripe for fertilization.
Most of the hay fever trees have specialized appendages to aid in carrying out the spread of their pollens. The appendages are called catkins and they look like elongated caterpillars. Clusters of unisexual tree flowers are retained in these catkins. When the flowers are ripe the catkins, swinging in the wind, discharge their pollens directly into the air. Some of these lightweight tiny pollens land on the ripe female flowers, of neighboring trees of the same family. In this way ovules are fertilized and seeds are formed which later fall to the ground. With favorable conditions a new tree develops from some of the seeds on the ground.
From the chart (Fig. 3) showing the pollination periods of the important hay fever trees, you can see that they shed their pollens over periods varying from ten days to twenty-four days. The average number of days being six-teen. However, studies have shown that the pollens, for . a particular kind of tree, reach a peak of concentration sufficient to cause symptoms in a person of average sensitivity, for only two to four days. Unusually sensitive per-sons suffer for longer periods.
The dates of pollination given in the chart are not of course absolute. They vary from one locality to another and on occasion from one year to the next. For example, in a pollen counting study of a part of New York City, Wodehouse observed the oak pollen to reach its peak of concentration a week earlier in 1931 than in 1932. In the South some trees pollinate from four to six weeks earlier than in the colder western states.
It is not practical to include here a list of pollinating dates for all trees in every locality. But such charts for each state are available upon request to local Drug Companies that prepare pollen extracts. The following section is intended as a general aid to becoming acquainted with the hay fever trees in your neighborhood.