380 Annals of the Carnegie Museum. 



The Fotamogetofi Formation. 



The Potamogeton formation has here almost precisely the same struc- 

 ture as described for the climax stages in the ponds of the peninsula 

 proper, for instance in the Chimney Ponds. 



The Castalia-NymphcEa Formation. 



This formation is comparatively a strong one in the pond. Its 

 structure is typically as follows : 



Fades. — 



Nymphcsa advena, Castalia tuberosa. 



Principal Species. — 



Pontederia cordata. 



Secondary Species. — 



Brasenia schreberi, Potamogeton natans, 



Naias flexilis, Myriophyllum spicatum, 



Utricularia vulgaris, Philotria canadefisis, 



Vallisneria spiralis. 



There is a tendency here as elsewhere to the segregation by zona- 

 tion of an inner Castalia consocies, including some of the Potamo- 

 getons, and an outer Nymphcsa consocies, including the Pontederia 

 cordata society. 



The Decodon-Persicaria Formation. 



The Decodon-Persicaria formation is very closely similar in eco- 

 logical structure to the corresponding formation in Stage I described 

 above, excepting that the Decodon.-z>e?iicillatus con^ocit^ is but weakly 

 developed. In Stage I the formation contains a number of secondary 

 species, which probably more properly belong to the Scirpus-Typha 

 formation, but which have been crowded forward by the shrub-zones. 

 On the lakeward side of the pond there has been no crowding for- 

 ward in this manner, and there is a clearly defined zone similar to the 

 Typha-Scirpus formation of the earlier stages of the succession, although 

 somewhat more complex in composition. 



The Typha-Scifpiis Formation. 



The structure of this formation around Pond Z is typically as 

 follows : 



