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maples. They begin flowering in March or April with the silver 

 maple, followed by the red, sugar, Norway, and three-leaved 

 maples, ending up with the sycamore maple toward the end of 

 May. Of all these, however, only the three-leaved maple is 

 strictly wind pollinated, and it is the only one of which the 

 pollen gets into the air in any great abundance. Perhaps this is 

 why the maples claim relatively few victims during their ex- 

 ceptionally long flowering season. 



The worst hayfever trees of all in the eastern states are the 

 birches and oaks. They both flower in our region in May. The 

 birches begin about the first of the month. Each species has 

 only a short flowering period, lasting generally less than a week, 

 but all together they extend through most of May. In our region 

 the first to flower are the cultivated European birches, mostly 

 Betida alba, followed by the native gray, yellow, and black 

 birches {B. popidifolia, B. lutea and B. lento). Before the birches 

 have finished flowering the oaks begin. All of the numerous 

 species of oak that we have in our region flower at very nearly 

 the same time so that the entire flowering period of the oaks 

 lasts only about two weeks. This always occurs in May but 

 varies with the season, sometimes beginning in the first week 

 and sometimes the second. Both the birches and oaks are prolific 

 pollen shedders. As a consequence their victims often suffer 

 severely. 



Before the tree hayfever season is over the late spring or 

 early summer season begins, in our region about the first of 

 May. This type of hayfever is almost entirely due to grasses 

 and these, unlike the trees of the previous season, are so closely 

 related that if a person is susceptible to the pollen of one he is 

 likely to be susceptible to that of them all. The season is 

 heralded in by the flowering of sweet-venial grass. This is not 

 quite the first grass to flower; the so-called annual blue grass 

 {Poa annua) springs up from its roots of the previous season 

 several weeks ahead of sweet-vernal grass, flowering sometimes 

 even in March, but not until the sweet-vernal grass comes into 

 flower do hayfever patients feel any discomfort from grass 

 pollen. Toward the middle of May June grass and orchard grass 

 begin to contribute their pollen to the air, and reach their 

 maxima during the first week in June; these two grasses are 

 accountable for nearly all the hayfever during the latter part of 



