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THE AMERICAN NATURALIST [Vol.L 



subgenera, namely Chamcenerion, distinguished, among 

 other features, by its distinct pollen grains; and Epi- 

 lobium proper having its pollen grains in groups of four. 

 E. angusti folium belongs to the section Chamcenerion, and 

 in the southern part of Canada and the Northern States 

 has no allied species except in mountainous regions (e. g., 

 mountainous Quebec and Colorado). Acting on the sug- 

 gestion supplied by Miss Holden's discovery, Mr. C. A. 



Forsaith, one of my graduate students, has investigated 

 the conditions of sterility found in species of Epilobium 

 belonging to the section of Chamoenerion. Through the 

 kindness of the Gray Herbarium of Harvard University 

 he has been able to study some two hundred specimens 

 from various geographic regions. The conditions in Epi- 

 lobium (Chamoenerion) angustifolium in the northern 

 part of its range, where it coincides in distribution with 

 its allied species, E. latifolium, are most interesting. 

 Nearly nine tenths of the specimens showed the pollen to 

 be imperfect. In contrast, the material from the southern 

 limits, where E. angustifolium does not coincide in distri- 



