83 



this group of ragweed relatives is the prairie ragweed or "Bur- 

 weedniarsh elder." Its correct name is Cyclachaena xanthiijolia. 

 Throughout much of its range which extends from Michigan to 

 Washington and southward to Oklahoma and New Mexico, it 

 is as important a cause of hayfever as any of the ragweeds. 



The ragweeds and their relatives constitute one of the 14 

 tribes of the composite famih-, the tribe most closely related to 

 the sunflower tribe. The connection between these two tribes 

 has been clearly established by George Bentham, the great 

 English botanist of last century and the greatest student of the 

 Compositae of all time. The complete interaction which aller- 

 gists have found between the pollen of the two tribes, and the 

 forms of their pollen grains proclaim their relationship. In fact 

 the morphology of their pollen grains shows that the ragweed 

 tribe may be regarded as a group of wind-pollinated derivatives 

 of the sunflower tribe. In spite of this there is a tendency among 

 modern botanists to treat the ragweed tribe as a separate 

 family, misled, perhaps, by the extreme modification in out- 

 ward appearance that these plants have sustained in response 

 to wind pollination. This treatment is misleading to allergists 

 because it removes the implication that the other members of 

 the composite family should be regarded as potential hayfever 

 plants, an implication that is abundantly sustained by experi- 

 ence. 



Another large group of Compositae — but in another tribe, 

 the Anthemideae, — is the group of sage brushes, wormwoods 

 and mugworts {Artemisia) . All of the many species of this huge 

 genus appear capable" of producing hayfever providing they are 

 abundant enough and their pollen sufficiently copious. In the 

 eastern states the few species of Artemisia which are found can 

 never be counted as more than minor contributary causes of 

 hayfever, but in the Prairie states and the Great Basin area, 

 where several species are much more abundant, the sage 

 brushes, mugworts and wormwoods are frequently primary 

 causes of hayfever. 



We have seen that all of the hayfever plants of this latter 

 season belong to the composite family. As with the grasses, the 

 ability to cause hayfever would seem therefore to be here a 

 family character. But what of the other Compositae, the asters, 

 daisies, coreopsis, thistle, and dandelion? We know that they 



