l6l] FLORA OF COLUMBIA AND VICINITY I9 



where the immersed foliage becomes much dissected. Some 

 characteristic species, like Typha latifolia, by occurring in the 

 wettest portions of swamps and swales, are integral parts of the 

 palustrous flora. There are six main associations: 



a. Amphibiae alismoides. The water-plantain asso- 

 ciation consists of broad-leaved amphibious plants with thick 

 spongy petioles, some leaves floating, others erect, while the im- 

 mersed leaves are reduced to bladeless phyllodes. There are 

 four characteristic species: 



Alisma Plantago Sagittaria variabilis 



Lophotocarpus calycinus S. platyphylla 

 (Swale near the covered bridge on the Rocheport road.) 

 These often form dense masses at the margins of ponds, 



and to them old ponds, as they fill up with the debris of aquatic 



vegetation, fall naturally a prey. 



b. Amphibiae typhoides. The cat-tail association of 

 tall plants with grass-like or equitant leaves stands in dense 

 ranks at the margins of ponds and in the wettest parts of 

 swamps. It is especially near to the palustrous vegetation. The 

 following are characteristic species : 



Typha latifolia Iris foliosa 



Acorus Calamus I. Virginica 



c. Amphibiae scirpoides. The bulrush association of 

 plants with almost, or altogether, naked culms, reaches its best 

 development in lakes, where the great bulrush, Scirpus lacustris, 

 is wont to stand in water of much depth. More's lake is 

 developing such a flora, and thus exhibits a tendency toward 

 a proper lacustrine vegetation. In ponds this association passes, 

 through the various species of Heleocharis, into the limose 

 spikerush association. These are typical species: 



