IOWA ACADEMY OF SCIENCES. 169 



Other plants of like character also appear under such 

 conditions. 



Sagittaria variabilis . Alismago Plantago var. 



Iris versicolor . Americana . 



Typha lati folia . Carex Sps . 



At least the Jr/s, Tijplin, and Scirpus laciistris may occur 

 in places that during later summer are entirely dry. These 

 plants on the one hand are deep rooted as in Scirpus or 

 have thick root-stocks as in Iris. When not covered by 

 plants the ground often becomes very hard. On the disap- 

 pearance of the early vernal plants, the ground soon 

 becomes covered with a thick growth of late summer and 

 autumn plants. The ground is thickly covered towards 

 the center and margins of the bayous. Of spring and early 

 summer plants under the shade of Salix anu/gdaloides, Polij- 

 r/onitni r/fre is a dominant plant. The Boltonia asteroides isone 

 of the most conspicuous of later plants, and along with it 

 Venioniafasciculata which, however,is more mesophy tic than 

 Baldivinia. Conspicuous later vernal plants here are Veron- 

 ica peregrina, and En'r/eron annuKS. The bayous with the 

 continual deposit of alluvium sand and dirt and the decay 

 of the hydrophytic and mesophytic plants or other mate- 

 rial washed in gradually becomes filled up, so that a 

 change in the character of plants occurs. The Salix amyg- 

 daloides is the only tree found in these situations. When 

 these slow-running streams are filled up with vegetable 

 detritus and inorganic material they die and the alluvial 

 prairie appears. In this alluvial flood plain many plants 

 are common to those of the upland prairies. The alluvial 

 prairie is rich in grasses although there are but few species. 

 Fresh water cord grass, Spartina cijnosuroides is conspicu- 

 ous. The rhizomes of the grass are often two feet long. 

 This is essential for the plant as it prevents washing the 

 plant away. There are times when a good part of this 

 flood plain has been under water for several days at a time. 

 Here, too, Rumex altissimus is a dominant type. 



Vernonia fasciculata. Helianthus maximiliani. 



• . Of the annuals. 



Helianthus annuus . Panicuin crus-galli . 



Euphorbia maculata . Euphorbia serpens . 



12 I AS 



