77 



In the first group are Verbena striefa, StropJiostyles helvola, Monarda 

 punctata, Froelichia floridana, Oenothera rJwnihipetala, and Lepid- 

 ium virginicnni. The second is represented by Digitaria Uliformis, 

 Trifoliiun pratcnse, Trifoliuni re pens, Poa pratensis, Verbasciim 

 Thapsus, Hordeum pusillnni, Antheniis Cotula, Brigeron caiiadensis, 

 Polygonum erectuni, Polygomtni ainculare, Achillea MiUefoliuni, 

 Plantago Rugelii, and Cheno podium album. 



In the Oqnawka area Populus alba, Gleditsia triacanthos, and 

 Robinia Pseudo-Acacia are frequently planted along the roadsides, 

 and shelter a number of more mesophytic species, such as Solanum 

 nigrum and Phytolacca decandra. 



In cultivated fields the weeds are composed mainly of introduced 

 species and of those natives of the original bunch-grass which are 

 readily propag'ated by seeds, thus including most of the interstitials 

 and but few of the perennials. In the Hanover area the most abun- 

 dant are Lepidiu.m virgiuicum and Rume.v Acetosella. Under certain 

 conditions which could not be determined Euphorbia corollata and 

 Pentstemon hirsutus come up in great abundance in almost pure as- 

 sociation. A square meter taken at random contained 605 plants of 

 the former species, and Pentstemon grows almost as densely. Other 

 abundant weeds are Monarda punctata, Hedeoma hispida, Silene 

 antirrhina, Specularia perfoliata, and Diodia teres. In the Havana 

 area, where the prickly-pear, Opuntia Rafinesquii, is common, it fre- 

 quently becomes a bad weed in corn fields. Cultivation does not kill 

 it, but merely serves to break the plant up into joints and scatter it 

 over a wider area. In the Oquawka area many fields are cultivated 

 some years and abandoned others, and they always contain a heavy 

 growth of weeds. One such field was almost carpeted with Cenchrus 

 carolinianus, above which arose the yellow-flowered stalks of Oeno- 

 thera rhombipetala in such numbers that from a distance the whojie 

 field looked yellow. The other weeds with them were Mollugo verticil- 

 lata, Strophostyles lielvola, Polanisia graz'coleus, I pom oca hederacea, 

 Croton glandulosus, var. septentrionalis, Xauthium commune, Brig- 

 eron canadensis, Ambrosia art emisiae folia, Solanum carolinense, Lc- 

 pidium virginicum, Cy perns Schweinit::ii, Asclepias amplexicatdis, and 

 Ambrosia psilostachya. This field had been in corn during the pre- 

 vious year. 



SUCCESSIONS FROM THE BUXCII-GRASS ASSOCIATION 



The bunch-grass association just described belongs typically to 

 the Prairie Province. Of the various associations composing the 



