376 Annals of the Carnegie Museum. 



Around R, before the vegetation was destroyed by the laying of 

 the waterworks intake-pipe, there appeared some intensely interesting 

 examples of alternation between different formations. There may 

 have been disturbances within recent years due to the washing in of 

 water from the bay or the lake, either of which is but a few feet dis- 

 tant from the pond. At any rate there are three formations repre- 

 sented in the zone between the Castalia-Nytuphcea formation and the 

 CephalantJms- Cornus formation : viz., the Decodon-Persicaria forma- 

 tion, the Sphagmwi-Oxycocciis formation, and the Scirpus-Typha 

 formation. The relative positions of the Sphagnum- Oxycoccus zxiA 

 Cephalanthus- Cornus formations are here just the reverse of what they 

 .are around Cranberry Pond, although they must be regarded as 

 occupying more typical positions around Cranberry Pond. Of the 

 three alternating formations mentioned above the Decodon-Persicaria 

 formation must be regarded as the normal formation. The Sphagnum- 

 Oxycoccus formation is an intercalated formation, representing normally 

 a stage in another succession, v/hile the Scirpus-Typha formation 

 normally represents an early stage in the succession under considera- 

 tion, its presence here being probably due to the inwashing of fresh 



^and. 



The Cephalanthtis- Cornus Formation. 



The perennial tangle of vegetation in the Decodon-Persicaria zone 

 is well adapted to catch and hold any vegetable debris blowing in 

 from the surrounding forest or floating on the surface of the pond. 

 This, together with the accumulation of vegetable matter derived 

 directly from the plants of the formation itself, gradually builds up 

 the soil to such a level that conditions become suitable for the ecesis 

 of the shrubs of the Cephalanthus- Cortius formation. 



The structure of the formation here is essentially the same as that 

 •described for the formation under Stage H, excepting that the Cepha- 

 lanthis-occidentalis consocies is more prominent, and the number of 

 secondary species is reduced by the disappearance of some of the 

 more hydrophytic species — as Proserpinaca palustris and JVymphcea 

 .advena. 



The Rosa Carolina consocies is also more clearly defined and can 

 be seen to show a decided preference for the shoreward zone of the 

 habitat. A little pond at the west end of Long Pond has been en- 

 >tirely filled in, and the only trace of the Cephalanthus- Cornus forma- 

 tion to be seen is a Rosa Carolina consocies, which is being killed out 

 ,by the shade of the encroaching trees. 



