PAPERS ON BIOLOGY AND AGRICULTURE 171 



THE INTRODUCED WEED FLORA OF ILLINOIS 



Henry T. Daelington, Michigan State Agricultural 

 College, Lansing, Michigan. 



The more one studies the weed flora of any territory, 

 the more one becomes convinced that there are two 

 classes, a native and an introduced weed flora. The first 

 class depends especially on the extent to which equili- 

 brium has been disturbed and therefore it often becomes 

 largely a matter of judgment as to what shall be con- 

 sidered a weed. This class varies with the community 

 and the conditions. Especially does it represent a re- 

 sponse to changed edaphic conditions. This is illustrated 

 by such plants as Witchgrass (Panicum capillare), native 

 species of Smartweed, Ragweed, and Cocklebur. There 

 is no question as to whether the above plants should be 

 classified as weeds, but the case is quite otherwise with 

 such plants as Asclepias uicarnata, Helenium autumnale, 

 Apocynum androesimifolivm and Sahatia angularis, all 

 of which are mentioned as weeds in a prominent weed 

 manual. Many others occur which are weeds only under 

 certain conditions. The consideration of this class of 

 weeds is a problem in itself. In the second class, which 

 contains the majority of weeds in any section, the indi- 

 viduals are finding their balance in a new flora, rather 

 than acting directly as a response to altered edaphic 

 conditions, though they are undoubtedly fostered by 

 these conditions. This is the class that is discussed in 

 this paper. The problem of weed introduction into the 

 state becomes a part of the larger problem of plant in- 

 troduction because any foreign plant may be potentially 

 a weed ; and in order to appreciate the development of 

 this flora in Illinois, it becomes necessary to examine 

 records extending over nearly a century. 



In 1794, Andre Michaux visited what is now the state 

 of Illinois, in search of plants, and in his Flora Boreali- 

 americana which appeared in 1803, he listed a number 

 of plants as having been found ''in regione Illinoensis.'* 



In 1826, L. C. Beck, writing in Silliman's Journal, 

 later known as "The American Journal of Science and 



