Jennings : A Botanical Survey of Presque Isle. 373 



Ponds. The species are not always the same in the corresponding 

 formations, but they are usually closely similar in ecological structure, 

 and are quite often nearly related systematically. 



The Chara Formation. 

 In basins with a clay or alluvial bottom, the deeper portions are 

 generally occupied in the Great Lakes region by a Chara formation, 

 which with certain of the Cyanophyceae may eventually result in the 

 deposition of more or less marl.'* As was stated in the discussion of 

 the Potamogeton formation of Cranberry Pond, Chara has been found 

 to prefer clayey or alluvial pond-bottoms to sandy ones, but, as the 

 plant was collected in Pond U together with Alyriophylluut and Naias, 

 it can be assumed to be present in the other Chimney Ponds also. 



The Potaviogeton Formation. 



The Potamogeton formation is well developed in all of the Chimney 

 Ponds and, as represented there, the vegetational structure is typically 

 as follows : 



Fades. — 



Potamogeton pectinatus, Potamogeton loticliitis, 



Potamogeton heterophyllus. 



Secondary Species. — 



Potamogeton lucens, Potamogeton natans, 



VaHisneria spiralis, Phi/otria canadensis, 



Naias flexilis, Myriophyllum spicatum, 



Letnna minor. 



This formation, as listed, may be taken as representative of the 

 mature Potamogeton zone whether at Presque Isle ; Brush Lake, Ohio, 

 where Potamogetoti zostercpf alius, Potamogeton lucens, Ceratophyllum 

 demersum, Myriophyllum, and Chara, are listed as typical species ; " 

 or in the Three Sister Lakes, Michigan (near Ann Arbor), where 

 Potamogeton lucens and Potainogeton zostercefolius are facies.*" 



'^ Davis, C. A. "Contribution to the Natural Plistory of Marl." Jourti. Geology, 

 8 : 485, 1900, and "A Second Contribution to the Natural History of Marl." 

 Journ. Geology y (): 491, 1901. 



'^ Schaffner, J. H., Jennings, O. E., and Tyler, F. J. /. c, pp. 153-154. 



soWeld, L. H. "Botanical Survey of the Huron River Valley, II. A Peat 

 Bog and Morainal Lake." Bot. Gaz., 37: 39-40. January, 1904. 



Reed, H. S. " Botanical Survey of the Huron River Valley, I. The Ecology 

 of a Glacial Lake." Bot. Gaz., 34 : 129. 1902. 



