112 PASTORAL AND AGRICULTURAL BOTANY 



The President of the American Hay-Fever Prevention Association 

 states that about one per cent, of the population of the United States 

 suffers from the disease. As he believes that the external cause is J;he 

 pollen of various plants, the extermination of these plants would result in 

 the practical elimination of hay-fever. Various plants give rise to pollen 

 grains in sufficient number to provide the irritating material cause of hay- 

 fever. Such are the rose, rye, sweet vernal grass (Anthoxanthum odora- 

 tuni) sweet-scented soft grass (Holcus odoratus}, meadow grass, Indian 

 corn, barley, wheat, oats, bean flowers, lilies, elder bushes in bloom, the 

 goldenrods, hay, timothy, spiny amaranth, marsh elder, yellow dock, 

 Johnson grass and cockle-bur. E. Philip Smith enumerates the principal 

 hay-fever plants. The hay-fever plants par excellence are the common 

 ragweed (Ambrosia artemisicefolia) , great ragweed (Ambrosia trifida) and 

 western ragweed (Ambrosia psilostachya} . These plants are widely dis- 

 tributed and blossom in late August and early September, producing an 

 abundance of wind-carried pollen. Perhaps more cases of hay-fever are 

 due to these plants than all others put together. v 



Common Ragweed (Ambrosia artemisicefolia). This is a native, 

 annual, branching plant growing about two to three feet tall. It has 

 thin leaves, bipinnately divided and racemes of numerous staminate 

 heads with chaffy receptacle. The pistillate heads are clustered. The 

 plant is found from Nova Scotia to British Columbia, Florida and 

 Mexico. 



Great Ragweed (Ambrosia trifida). This is an annual plant with hir- 

 sute to hispid stems, 1-5 meters tall, and opposite, deeply three to five 

 lobed leaves with serrate margins. The racemes of staminate heads are 

 5-15 centimeters long with saucer-shaped involucres, while the pistillate 

 heads are clustered in the axils of the leaf-like bracts. The great ragweed 

 occurs in the rich alluvial soil along streams in moist, meadow soils from 

 Quebec to Northwest Territory, Florida, Arkansas and Colorado. The 

 third species of ragweed, Ambrosia psilostachya ranges from Northwest 

 Territory to Illinois, Texas, Mexico and California. Artemisia heter- 

 ophylla of California may also be classed with the hay-fever inducing 

 plants. The results of experimentation with various kinds of pollen have 

 been most discordant. As the digestive power of the nasal mucosa is 

 very slight and the pollen-grain is effectively sealed, it is difficult to 

 understand how any of the protein-contents could diffuse out passively. 

 The affects of the possible germination of pollen in the nasal passages may 



