ECOLOGICAL CROSS SECTION OF THE MISSISSIPPI. 189 



and river islands. Salix longi folia and Populus monilifera 

 arc represented by numerous seedlings. There is, of course, 

 no spring flora. Plants ordinarily occur as isolated indi- 



viduals. 



number 



here than on the islands. Among the plants encountered 

 are Cay sella Bur sa-pastoris , Cardiospmnuvi Holicacabum, 

 Rotala ramodor, Jussieua repens, Ambrosia trifida, Bidens cer- 

 nua, B. chrysanthemmdes, B. connata, Erigeron annuus, E. 



osu 



Helenium autumnole, Iva ciliata, Pluchea camphorata, Datura 

 Stramonium, D. Tatula, Solanwn carolinense, S. nigrum, 

 Gratiola sphaerocarpa, G. virginiana, MimuLus alatus, Vero7i- 

 ica peregrina, Lippia lanceolata, Acnida tuberculata, Euphorbia 

 humistrata, E. Preslii, Polygonum Ilydropiper, P. hydropiper- 

 oides, Cyperus aristatus, C. diandrus, Diplachne fasdcularis, 

 Eragrostis reptans and Paspalum fluitans. This flora disap- 

 pears with the advent of the high water and all seed is washed 

 away. Since the position of the mudflats is continually 

 changing, it is clear that for a fresh supply of seed an external 

 source must be relied on. AVhile several of the plants bear 

 seeds which are fitted for transportation by wind, it is prob- 

 able that the seed of many of these species as well as of others 

 is derived from the debris brought down each spring in large 



quantities. 



The Illinois shore. 



The sandy shore on this side supports but a scant vegeta- 

 tion. Solix longifolia and Populus monilifera are never ab- 

 sent. Different herbaceous plants arc added during the year. 

 Characteristic are Oenothera biennis, Xanthium canadense and 

 Plantago patagonica aristata. Polygonum aviculare and P. 

 erectum make their appearance as do Cyperus acuminatus, 

 C. aristatus, C. diandrus, C. Schwdnitzii, C. spedosus and 

 C. striqosus. Less important though still fairly numerous 



Nasturtium ohtusum, N 



cuspidatum 



and D. paniculatum, Tri folium hyhridum and Verhascum 

 Thapsus. Compositae are prominent in the latter part of 

 the year. The most important are Artemida ludoddana, 

 Bidens connata, Coreopds aristosa and C. anstosa mutica, 



