ECOLOGICAL CROSS SECTION OF THE MISSISSIPPI. 



167 



It 



be noted that Hydrastis canadensis forms 



patches to the exclusion of all other species, as is true to 

 some extent of Arisaema triphyllum, Polygonatum giganteum 



racemosa. Oxalis violacea ordinarily occurs 



Smiladna 



The aerial 



forms 



singly. Occasionally Passiflora lutea is met with, 

 portion of most of the plants just mentioned dies ^ 

 fall, leaving the sinkhole comparatively bare, 

 a great contrast with the sinkholes occurring in the open plain. 

 Here again dry and wet sinkholes are to be considered. The 

 dry sinkhole in the plain is usually surrounded by shrub- 

 bery, composed chiefly of Euonymus atropurpureus, Staphylea 

 trifolia, Rhus Toxicodendron, Pyrus coronaria, Samhucus 

 canadensis and Rihes gracile, through which Vitis cordifolia 

 twines. Occasionally a few oaks or hickories or a sohtary 

 Platanus ocddentalis overtop the shrubbery, evidently a sur- 

 vival from a period when the drainage of the sinkhole was 

 temporarily interrupted. The inner, upper portion of the 

 sinkhole usually accommodates numerous smaller, stunted 

 specimens of Ribes gracile together with briars and brambles. 

 The central portion of the sinkhole is ordinarily bare, the 

 water which at each rain rushes past to escape through the 

 fissure, sometimes as much as two feet in diameter, prevent- 

 ing the estabhshment of any plants. On the sides are found 

 occasional specimens of Arisaema Dracontium, Arisaema 



triphyllum and Smiladna racemosa. 



frequent 



Hydrastis 



woods, is ordinarily met with here. Nor are the ferns which 

 frequent the latter encountered. 



On 



ft. 



one 



When, as frequently happens, 

 of the edges of a sinkhole in the open plain is bare of 



shrubbery, Hypericum 



The wet sinkhole in 

 pond, has a, flora disti: 



folium are found during the summer months. 



) familiar as a wooded 



mor 



Wooded ponds. 



Here 



of small ponds which arc the result of the obstruction of 

 the drainage of sinkholes. As a result, not only is the sink- 



