168 MISSOURI BOTANICAL GARDElSr 



hole filled with water but the latter also accumulates over 

 the ground which immediately surrounds the sinkhole and 

 which ordinarily has a slight slope towards it. It is evident 

 that the water will continue to encroach upon the ground 

 till an equilibrium shall have been established between the 

 water supply and the evaporation. Ordinarily the wooded 

 ponds arc therefore quite shallow with the exception of an 

 area of great depth at or near the center. Hence we never 

 find the central portion occupied by plants whose roots pene- 

 trate the mud, but by floating forms only. 



Wooded ponds permit the growth of the more water-lov- 

 ing species of oak^ occasionally associated with specimens of 

 Platanus occidentalis (plate 12, 1). The larger amount of 

 light permits the existence of numerous shrubs which, how- 

 ever, belong to comparatively few species, Staphylea trifolia 

 being prominent at some distance from the water, where 

 Cephalanthus occidentalis is abundant. Vitis cordifoliay 

 Vitis ripariay Rhus Toxicodendron, Smilax herbacea and S. 

 hispida are the principal creepers. 



The herbaceous flora is a distinct rosette formation, the 

 xerophytic character possibly being due to too great an 

 amount of water in the soil, interfering with the necessary 

 life processes. This is borne out by the opinion expressed 

 by Nillson* quoted by Coultcr.f The principal components are 

 Arctium Lappa minus, Solidago Drummondii, S. canadensis^ 

 S. nlmifolia, Erigeron canadensis and Brunella vulgaris. As 

 to th(^ hydrophytic flora, Heteranlhera limosa and Pontederia 

 cordata together with Jassieua rcpens on the one hand, and 



Lemna perpusilla and Woljfia punctata on the other, are 

 the principal species. The presence of large quantities of 

 Riccia natans must also be mentioned. 



In sharp contrast to the wooded pond stands the open 

 pond, i. e. the wet sinkhole in the field. All woody plants arc 

 absent with the exception of an occasional specimen of 

 Cephalanthus occidentalis. The main flora around the wet 



* Nillson, H. Einigcs ueber die Biologic der schwedisclien Sumpfpflan- 



zen. Bot, Centralbl. 76 : 9. 1898. 



t Coulter, S. M. An Ecological Comparison of some Typical Swamp- 

 Areas. Rcpt. Mo. Bot. Card. 15 : 39. 1904. 



K 



