yo UNlVERSITlf OF MISSOURI STUDIES [2X2 



vense), and the rye (Secale cereale). In fields of rye the bar- 

 ley (Hordeum sativum hexastichon) is a common weed. The 

 chesses about low places and along roads consist of Bromus 

 secalinus, B. mollis, B. racemosus, and B. tectorum. The char- 

 acteristic weed of stubblefields is Erigeron Canadensis. 



d. Ruderales helianthoides. The sunflower associa- 

 tion of weeds of low grounds reaches its full development in 

 late summer and autumn. It is found in low waste grounds. 

 In neglected cornfields, especially where the corn has been 

 drowned by floods, this association is seen most clearly. It con- 

 sists of smartweeds {Polygonum spp.), and a host of autumnal 

 composites, such as species of Helianthus, Ambrosia, Coreop- 

 sis, Bidens, and Xanthiiim. Certain grasses, such as Panicum 

 proliferum, P. capillare, and P. Crus-galli, and the nut-grasses 

 (Cyperus spp.) are common. 



e. Ruderales pharbitidoides. The morning glory as- 

 sociation in cornfields consists of herbaceous lianas, such as 

 Pharbitis hispida, P. Nil, Polygonum scandens, and P. 

 Convolvidus. The tall maize plants furnish fit hosts for these 

 twiners. Certain cucurbits, especially Sicyos angulata, occur 

 also. 



f. Ruderales amarantoides. The pigweed association 

 is universal in gardens, corn and potato fields, and in unswarded 

 waste grounds. It consists of the numerous species of Amaran- 

 tus, Chenopodium, Setaria, Eragrostis, Panicum, and Eleusine. 

 With these occur almost every weed of the region as well as 

 many escapes from garden and field. This association flourishes 

 best in rich well manured soil, but it is common even in the 

 poorest grounds. 



g. Ruderales portulacoides. The purslane associa- 

 tion, like the preceding, prefers gardens and cornfields. It con- 



