Vol. XVI, pp. 91-98 June 25, 1903 



PROCEEDINGS 



OF THE 



BIOLOGICAL SOCIETY OF WASHINGTON 



THE HAWTHORNS OF NORTHEASTERN WISCONSIN. 



BY J. H. SCHUETTE. 



The genus Crataegus is variable and has always given trouble 

 to field botanists. As a result of deficient material and imper- 

 fect observations there is a confused treatment, even in leading 

 manuals, and this may be the cause of the excessive splitting of 

 species in recent years. There are six distinct species or rather 

 groups in northeastern Wisconsin each including forms which 

 are not entitled to specific rank although exhibiting some con- 

 stant differences. These variant forms should be considered 

 only as subspecies. Hawthorns, like roses, willows, oaks and 

 many other woody plants furnish valuable material for research 

 to evolutionists, who have hitherto turned their attention chiefly 

 to the animal kingdom. The variability and polymorphism are 

 due to the influence of the evironment and soil, the climate, ef- 

 fects of age and in j ury, crossing, and progressive heredity. In the 

 region of Green Bay, where the retiring waters of bay and lake 

 left distinct evidences of former higher levels in Pleistocene and 

 Recent geological time, variation due to changed environment is 

 illustrated especially by the wild roses. Thus individuals grow- 

 ing on the younger formations of moist and wet sand, or near 

 the surf, present characters plainly different from those of others 

 of the same species growing on the higher alluvial or Pleisto- 

 cene ridges. Crataegus like Rosa is very susceptible to such 

 25— Peoc. Biol. Soc. Wash. Vol. XVI, 1903. (91) 



