182 ILLINOIS STATE ACADEMY OF SCIENCE 



nial. The total number of introduced species listed above 

 is 256. Undoubtedly there are several others which should 

 be included. These figures, however, will serve as a basis 

 for estimating the relative weed introduction from vari- 

 ous sources. On this basis, 73% are of European origin, 

 14% come in from West of the Mississippi, 6% are of 

 Tropical American origin, 5% are of Asiatic origin, and 

 2% are cosmopolitan. As to duration, approximately 

 32% are perennial, 60% annual and 8% biennial. Every 

 species from Tropical America without exception acts 

 here as an annual, which is to be expected. 



The greatest number came in during the period from 

 1872 to 1897. Apparently the number of introductions 

 during the last 24 years have been 30% less than tlie 

 number during the preceding 25 years, the average be- 

 ing 2.4 per year as against 3.3 yearly for the preceding 

 interval. The period from 1872 on no doubt represents 

 a rapid settling up of the farmlands of the state, and is 

 naturally correlated with the introduction of many new 

 species. The observations of Dr. H. S. Pepoon, one of 

 the most thorough-going students of the flora of the state, 

 are in line with this supposition. In 1876 he noted 355 

 species in a certain farm, and on the same farm in 1904, 

 only 200, and these, he says, in his observations at the 

 time ''are the plebians, toughs, tramps, and rabble. The 

 royal ones are gone." 



Acknowledgements are due Dr. Chas. F. Millspaugh of 

 the Field Museum for most of the articles consulted in 

 reference to the flora of the state. The work was done 

 under the direction of Dr. H. C. Cowles, of the University 

 of Chicago. 



BIBLIOGRAPHY 



1803 Michaux, Andre, Flora Boreali-americana. 



1826 Beck, L. C, Catalogue of the Plants of Illinois. Silllman's 

 Journal (Am. Jour, of Science and Arts). Vols. 10 and 11. 



1844 Babcock, H. H., Flora of Chicago and Vicinity. The Lens, vols. 



1 and 3. 

 Engelmann, Geo., A List of the Plants Collected in Illinois and 

 Missouri by Chas. A. Geyer. Am. Jour. Sci. and Arts vol. 44. 



1845 *Short, C. W., On the Botany of Illinois. Wesiern Jour, of Medi- 



cine. 



• Note: The starred references were not consulted. 



